Identifying Valves Used in Sigma Products (SB1001.01)

Service Bulletin #SB1001.01
Identifying Sigma Valves
1817 John Towers
El Cajon, CA 92020
619.258.3700
Before you start -
If you have a valve with a label on the coil that
includes a valve number and you are confident
that the valve is compete and original - skip to
page 23 for valves by part number.
This bulletin is provided to allow you to identify most
of the valves and parts used in both mechanically
refrigerated (refer) and cryogenically cooled equipment.
If you already know some basic information
about your valve, you will likely need to use only a
small part of this bulletin. Conversely, if you have a
box of valves and parts, and/or you are working with
equipment that has been modified over time, you may
need to use this bulletin to follow a somewhat tedious
path to correctly identify what you have.
This bulletin is designed to help you identify the
valve you have. It is not a service and repair bulletin.
See SB1002 for Troubleshooting Cryogenic Coolant
Valves in Temperature Chambers, SB1004 for Troubleshooting
Cryogenic Valves in Thermal Platforms, and
SB1003 for Valve Disassembly and Assembly instructions.
If you have a valve used in a refrigeration system
that uses compressors, start with page 2.
If you have a valve used in a cryogenic cooling
systems (L–N 2
or L–CO 2
), start with page 5.
If you have a valve of unknown use/origin, start with
page 15.
Terms and abbreviations to know for this document
“B” Refers to the smaller of two custom made Sigma valves
“D” Refers to the larger of two custom made Sigma valves
FNPT Female National Pipe Thread
L–CO 2
Liquid Carbon Dioxide
L–N 2
Liquid Nitrogen
MOPD Maximum Operating Pressure Differential - the maximum difference in pressure
between the valve inlet and valve outlet at which the valve can safely operate.
Orifice Is the small control hole in the valve body through which coolant passes on it’s
way to the chamber or platform
Refer Mechanically Refrigerated Cooling System
SB1001.01-1

Valves used in mechanical
refrigeration systems
Sigma Systems refrigeration systems have
used a variety of standard valves and some
custom made valves that are peculiar to
Sigma.
Sporlan
Parker
The standard valves shown in image 1-1 are
typically identified by their labels. Replacement
valves, coils, and sometimes parts,
for these industry standard valves are most
readily available from your local refrigeration
supply dealer.
Alco
Sporlan
Industry standard refrigeration valves
Image 1-1
Sigma has also used a variety of custom
valves built specifically for us. There are two
sizes as shown in image 1-2.
The smaller valve is known as a “B” size valve,
measures roughly 1¼” (32mm) in diameter
and 2³⁄₈” (60mm) tall. The larger valve is a “D”
size valve, it measures roughly 1⁵⁄₈” (41mm)
diameter and almost 3” (76mm) tall.
“D” size
“B” size
If you have a “D” size valve skip to page 4.
If you have a “B” size valve continue on
page 3.
D & B size valves
Image 1-2
SB1001.01-2

“B” size refrigeration valves
Until the summer of 2001 Sigma used modified “B”
L–CO 2
coolant valves for refrigeration (refer) service.
These valves were labelled B2023-S13 (image 1-3). If
the label is still intact, that number is all you need to
identify the valve – go to page 23.
About the summer of 2001, a new “B” size refrigeration
valve was introduced. These valves were labelled with
a Sigma number in the range of 35200-204. If the label
is still intact, that number is all you need to identify the
valve – go to page 23.
If your valve does not have a label on it, a newer valve
can be distinguished from an older valve by the wrench
flats on the sides of the body and an ID stamp on the
top of the valve body (image 1-4). The older valve does
not have wrench flats or ID stamp. You need to remove
the coil from the valve to see the top of the valve body.
If the body is stamped “RA” the valve is a 35200-204
refer valve. The older valve, B2023-S13, bodies have
no stamp.
Internally the two “B” refrigeration valves are not the
same. The B2023-S13 valves were sealed at the factory
with a special sealing material and technique. If these
valves must be opened in the field, the valve should
be replaced with a new Sigma refrigeration valve of the
35200-204 type. The new valves are more reliable and
are completely field serviceable.
Older style “B” valve labeled B2023-S13
does not have body stamp or wrench flats
Body
Stamp
Image 1-3
#35200-204 “B” valve
with body ID stamp and
wrench flats
Older style “B” valve
labeled B2023-S13.
Sigma 35200-204 “B”
valves have body stamps
and wrench flats.
Wrench
Flat
Image 1-4
Body ID
stamp
Wrench
Flats
Image 1-5
SB1001.01-3

“D” size refrigeration valves
Until the summer of 2001 Sigma used modified “D”
L–N 2
coolant valves for refrigeration service. These
valves were labelled D2024-S15. If the label is still
intact, that number is all you need to identify the valve
– go to page 23.
Body Stamp
About the summer of 2001 the “D” valves were
upgraded with larger wattage coils, larger internal
orifices to permit more flow and higher pressures,
and a new outlet port location. The new valves
were labelled with a Sigma number in the range of
35205-209. If the label is still intact, that number is all
you need to identify the valve – go to page 23.
If your valve does not have a label on it, a new “D”
size valve can be distinguished from an older valve by
the wrench flats on the sides of the body, an ID stamp
on the top of the valve body, and the outlet port on
the bottom. The older valve does not have wrench
flats, has no body stamping, and has the outlet on
the opposite side from the inlet. To see the body
stamping, you need to remove the coil from the valve
so you can see the top of the valve body.
“D” valve with body stamp
and wrench flats, 35205–209.
Wrench flat
Image 1-6
Because of the change in flow and pressure performance,
new valves may be substituted for old valves
with some plumbing changes, but not the reverse.
See SB1002 for Troubleshooting Cryogenic Valves
used Sigma in Thermal Chambers, SB1004 for Troubleshooting
Cryogenic Valves Used in Sigma Thermal
Platforms, and SB1003 for Valve Disassembly and
Assembly instructions.
Body stamp (not visible
in this picture)
Outlet
Wrench flats
Image 1-7
#32505–209 body – newer
“D” body with wrench flats
and Inlet on side and Outlet
on base, and body stamp.
D2024-S15 body – older “D”
body with Inlet on side and
Outlet on opposing side.
SB1001.01-4

Valves for cryogenically cooled systems
Sigma Systems Liquid Nitrogen (L–N 2
) and Liquid Carbon
Dioxide (L–CO 2
) cooled systems have nearly always used
custom made valves that are peculiar to Sigma Systems.
Sigma equipment built up to the early 1990’s used Sigma
designed valves built by ASCO. In the mid 1990’s Sigma
changed to an improved design that is custom built for
Sigma.
ASCO built Sigma valves are characterized by a small
valve body with a machined grove around the bottom
and a typically large green actuating coil housing. Newer
design Sigma valves are typically smaller, have a stainless
steel body and a black coil housing that is about the
same diameter as the body (image 1-8).
As of the writing of this bulletin, most parts for the ASCO
valves were still available from Sigma. The ASCO valves
typically have a label on the coil that identifies the valve.
If you call Sigma for parts, it will be very helpful if you
have the number.
ASCO valve on the left and two newer custom
designed Sigma valves.
Image 1-8
The design changes that accompanied the move away
from ASCO built valves resulted in valves that run quieter
and far longer.
The balance of this section deals with identifying these
more modern valves.
L–N 2
or L–CO 2
?
While Sigma L–N 2
valves look very similar to L–CO 2
valves (image 1-9), there are significant differences. If you
are certain that you know which coolant (L–N 2
or L–CO 2
)
your system uses, proceed with this section. The rest
of this section relies on your certainty. If you are not
certain which coolant your system uses, go to page 15 to
determine your valve type by analyzing it’s parts.
L–N 2
valves
On the surface L–N 2
and L–CO 2
valves
look very similar, inside there are significant
differences.
Image 1-9
Sigma has used a variety of custom L–N 2
valves. Size is
the first distinction you need to make. Image 1-10 shows
the two sizes. The larger valve is a “D” size valve, it
is roughly 1⁵⁄₈” (41mm) diameter and almost 3” (76mm)
tall. The smaller valve is known as a “B” size valve, it is
roughly 1¼” (32mm) in diameter and 2³⁄₈” (60mm) tall.
For “D” size L–N 2
valves skip to page 11.
“D” size
valve
“B” size
valve
For “B” size L–N 2
valves continue on page 6.
Image 1-10
SB1001.01-5

“B” size L–N 2
valve identification
The earliest “B” size L–N 2
valves used white o-rings for
plunger guide seals and had white faced plungers. The
valves had a 6w actuating coil and were rated at 175 psi
MOPD. These valves were labeled A2025-S26. These
valves were made until approximately 1998. The solid
white plunger guide o-rings were sometimes difficult to
seal and the white faced plungers were not as long lived
as expected.
The next “B” size L–N 2
valve used a Variseal for the
plunger guide seal and had red faced plungers. The
valves had a 6w actuating coil and were rated at 175 psi
MOPD. These valves were labeled A2025-S28.
In the late summer of 2001, a third generation valve was
introduced that used the same Variseal and red faced
plunger as the A2025-S28 valve, but featured a 8-9w
actuating coil that raised the valves pressure rating to
350 psi MOPD. These valves are labeled with Sigma
numbers in the range of 35100-104.
Important note: The plunger guide, body, and o-ring
seals of the A2025-S26 valve are not interchangeable
with either of the later valves that use a Variseal seal.
If your valve has a label on the coil AND YOU
ARE CERTAIN THE VALVE COIL HAS NOT BEEN
REPLACED AND/OR THE LABEL OR COIL IS NOT
FROM ANOTHER VALVE, then the number on the valve
is all you need to identify your valve – go to page 23.
If there is any chance that a replacement coil was fitted
to your valve thus changing the number, or if there is no
label on the valve, then you will need to open the valve to
look at the type of seal that is inside.
Image 1-11
SB1001.01-6

To identify the valve you must disassemble it. Start by
removing the coil nut and coil.
Caution: If resistance is felt when lifting the coil Do
NOT increase force to remove the coil. Use a small
screwdriver to gently lift it loose from the insulative
layer (See page 25 for more information).
The top of the plunger guide base should have two
small detents for opening the valve (image 1-12). Always
use the a proper spanner wrench or spanner nut that
engages the two detents to open the valve.
Spanner nut
(available
from Sigma)
DO NOT use a screwdriver in the slot at the top of
the plunger guide to open the valve (image 1-13).
NEVER use any type of tool that grips the center of
the valve guide (images 1-13a and 13b).
The guide is hollow, thin, precision machined and
easily distorted. Once distorted, it must be discarded.
It is very easy to distort the plunger guide.
Such distortion can easily lead to valve failure and
a “run-away” cold condition.
Detents for
spanner nut
If your valve does not have spanner holes, we recommend
that you replace the valve. The valve is of an older
design, A2025-S26, and has likely given all the service
that can be expected of it.
Image 1-12
Image 1-13
Image 1-13a
Image 1-13b
Do NOT use a screwdriver to loosen the
guide as this will distort the guide. Such
distortion can easily lead to valve failure
and a “run-away” cold condition.
NEVER grip the stem of the plunger guide
with pliers or wrenches of any kind, as this
can easily distort and ruin the hollow plunger
guide.
SB1001.01-7

Note: Spanner nuts for servicing valves are available
from Sigma Systems (image 1-14).
Spanner nuts are available from Sigma
Place the spanner nut over the valve guide as shown
in image 1-15, with the pins in the detents in the
plunger guide base, use a wrench to push down
and turn in one action (image 1-16). If the valve
is mounted in the temperature chamber or thermal
platform, use care to avoid bending mounting brackets,
plumbing, etc. If the valve is loose, the easiest way to
hold the valve is to use a short section of threaded ¹⁄₈”
brass or copper pipe in the inlet as a handle (image
1-17).
#35952 for larger “D”
valves
#35951 for larger “D”
valves
Image 1-15
Image 1-14
Image 1-16
Slide the spanner nut over the plunger
guide and align pin with detents.
Press down with a box end wrench and
turn in the same motion.
Image 1-17
Image 1-17a
If extra grip is needed to hold a body without wrench flats. Use a
short section of threaded ¹⁄₈” brass or copper pipe as a handle.
SB1001.01-8
With the wrench and pipe in the positions shown above,
squeezing the two “handles” will loosen the plunger guide.
With the wrench on the opposite side of the pipe, a squeezing
motion will tighten the plunger guide. Note: If you
use your other hand to squeeze the wrench onto the nut it
will prevent the nut from slipping out of the detents.

Check the plunger guide, the seal, and the valve body
to be sure of the type of valve and to be sure that no
one before you has used mismatched parts. (If you are
trying to solve a leak problem, there’s a good chance that
someone else may have put the wrong parts in the valve.)
Plunger guide: Note that the plunger guide for the
A2025-S26 valve has a tapered seat, while the plunger
guide made for use with the Variseal has a stepped seat.
Note stepped sides
verses tapered sides
Plunger guide for
Variseal for use with
S28 or S35100-104.
Image 1-18
Plunger guide for white
seal for use with S26.
Plunger guide for
Variseal for use with
S28 or 35100-104.
Plunger guide for white
seal for use with S26.
Image 1-19
Seal: The A2025-S26 valve uses a white
o-ring seal. The A2025-S28 and 35100-104
valves use a Variseal. The Variseal is flat
on the top and bottom and has a very small
visible stainless steel spring inside.
Image 1-20
“Variseal”
Plain o-ring seal
Image 1-21
Variseal shown with
correct plunger guide.
Solid o-ring seal shown
with correct plunger guide.
SB1001.01-9

Body: The body of an A2025-S26 valve
has an undercut ring at the base of the
threads to fit the o-ring. The later valve
bodies with Variseals do not have an
undercut. See images 1-22 and 1-23 on
ways to tell if the body has an undercut.
NOTE: It is imperative that all three
parts, the plunger guide, body, and
seal match. As the body is not changeable
without buying a new valve, replace
the plunger guide or seal if they are not
correct.
The valve body determines what kind of
valve you have.
If you have a valve that uses a Variseal,
then you have either an A2025-S28
valve or a Sigma series 35100-104
valve. There are two features of the
Sigma 35100-104 valves that differentiate
them from the A2025-S28 valve. The
35100-104 valves have wrench flats on
the sides of the body and an ID stamp
mark “NA” on the body. The A2025-S28
valves have neither of these features
(image 1-24).
S28 or 35100-104 body, note how
you can see virtually 100% of
the rim of the dime all the way
around.
S26 body, note how the rim of the
dime disappears under the undercut
in the body and there is a
larger gap at the top.
Image 1-23
Image 1-22
S28 or 35100-104 body, the
dime nearly falls out
S26 body, the dime hardly
moves
On the newer body type the
body stamp on a “B” size
L–N 2
valve will be “NA”
Wrench
Flat
Wrench
Flat
Image 1-24
Sigma 35100-104
Sigma S28
SB1001.01-10
To differentiate the A2025-S28 variseal valve from the newer 35100-104 variseal
valve, look for wrench flats and/or a body stamp. The 35100-104 valves has both,
the S28 valve has neither.

“D” size L–N 2
valve identification
“D” size L–N 2
valves made until approximately summer
of 2001 had ¹⁄₄” FNPT inlet and outlet ports located on
opposite sides of the valve body (image 1-25). These
valves had a ³⁄₃₂” orifice, a 10w actuating coil, and a
225 psi MOPD. The valves were labeled D2024-S15.
“D” size L–N 2
valves made after the summer of 2001
had these distinguishing characteristics:
There are wrench flats on the body
There is an ID stamp of “RB” on the top of
the valve body
Outlet port on the bottom, orifice is ⁵⁄₃₂”
The coil wattage is 13-14w.
“S15” Image 1-25
These later valves have a 350 psi MOPD.
The valves were labeled with Sigma numbers
in the range of 35300-304 (image
1-27 left valve)
Body Stamp
Wrench flat
“D” valve with body stamp
and wrench flats, #35300-104
Image 1-26
Wrench flats
Inlet
Inlet
“35300-104” valve
Outlet
Image 1-27
Outlet
opposite
inlet
“S15” valve
SB1001.01-11

L–CO 2
valve identification
Sigma has used a variety of custom L–CO 2
valves. There
are two sizes as shown in the image 1-28.
The smaller valve is known as a “B” size valve, measures
roughly 1¼” (32mm) in diameter and 2³⁄₈” (60mm) tall.
The larger valve is a “D” size valve, it measures roughly
1⁵⁄₈” (41mm) diameter and almost 3” (76mm) tall.
“D” size
“B” size
If you have a “D” size valve, skip to page 14.
“B” L–CO 2
valve identification
“B” size L–CO 2
valves are available in two pressure ratings,
300-350 psi MOPD, and 1000 psi MOPD. The only
difference between 300 psi valves and 1000 psi valves is
the size of the orifice in the valve. The 300 psi valve has
a ³⁄₃₂” orifice and the 1000 psi valve has a ³⁄₆₄” orifice.
D & B size valves
Image 1-28
The relative orifice size is readily apparent by looking
either at the outlet port on the bottom of the valve (image
1-29), or at the valve seat/orifice inside the valve if it is
open (image 1-30).
Valves made before the summer of 2001 were labeled
300 psi MOPD B2023-S13
1000 psi MOPD B2021-S9
If the label is still intact, that number is all you need to
identify the valve – go to page 23.
300 PSI orifice from
bottom
Image 1-29
1000 PSI orifice
from bottom
300 PSI orifice from
seat side
1000 PSI orifice
from seat side
Image 1-30
SB1001.01-12

Beginning late summer 2001, new valves were introduced.
The 300 psi MOPD valve was upgraded to 350
psi MOPD and both the 350 psi and 1000 psi valves had
wrench flats added to the valve body. The valves were
labeled as follows:
350 psi valve Sigma 35110-114
1000 psi valve Sigma 35120-124
If the label is still intact, that number is all you need to
identify the valve – go to page 23.
If you can’t find a label, you can check to see if the valve
body is ID stamped (image 1-32). The bodies of the
newer valves are stamped as follows:
350 psi valve “CA” is Sigma 35110-114
1000 psi valve “HA” is Sigma 35120-124
Sigma 35114 valve with label.
Image 1-31
The ID stamps on a “B” size
L–CO 2
valve will be “CA”
for 350 psi and “HA” for
1000 psi
Wrench
Flat
Wrench
Flat
Image 1-32
SB1001.01-13

“D” L–CO 2
valve identification
“D” size L–CO 2
valves are available in two pressure
ratings, 300-350 psi MOPD, and 1000 psi MOPD. The
only difference between 300 psi valves and 1000 psi
valves is the size of the orifice in the valve. For valves
built through the summer of 2001, the 300 psi valve
has a ³⁄₃₂” orifice and the 1000 psi valve has a ³⁄₆₄”
orifice. The relative orifice size is readily apparent by
looking either at the outlet port on the bottom of the
valve, or at the valve seat/orifice if the valve is open
(image 1-33).
Valves made until the summer of 2001 were labeled
1000 PSI ³⁄₆₄”orifice from
seal side.
300 PSI ³⁄₃₂” orifice
from seal side.
Image 1-33
300 psi MOPD D2013-S39
1000 psi MOPD D2011-S25
If the label is still intact, that number is all you need to
identify the valve – see page 23.
Beginning late summer 2001, new 350 psi MOPD
valves were introduced to replace the 300 psi MOPD
valves. The valve orifice was increased to ⁵⁄₃₂” to
increase flow and wrench flats were added to the valve
body. The valves were labeled as follows:
Body Stamp would be
“CB” on L–CO 2
valve
350 psi valve Sigma 35310-314
If the label is still intact, that number is all you need to
identify the valve – see page 23.
Image 1-35
If you can’t find a label, you can check to see if the
valve has wrench flats, or if the body is ID stamped
(image 1-35). The bodies of the new valves are
stamped as follows:
Wrench flat
350 psi valve “CB” is Sigma 35310-314
“D” valve with body stamp
and wrench flats, #35310-104.
SB1001.01-14

Identifying Loose Valves and Parts
This section presumes that you need to identify a valve, or valve
parts, that are loose and not installed in a system. Complete,
but unlabeled, valves will be the primary focus of this section,
but other parts will be identified as well further along. As valve
bodies are not sold as service items, the identification process
should start with the body.
The first thing to look for is a body stamp (image 1-35). (Body
stamps are on valves made after the summer of 2001.)
The body ID stamp
identifies the type of
valve body.
If the valve does NOT have a body stamp continue on page 16.
If the valve has a body stamp, use the chart below
Bod
ody
Valv
alve
Stam
tamp
Numbe
umber
S
ize
CA
35110-114
Small
CB
35310-314
Large
M
OP
D
Coolan
t
350
psi
–CO
L
2
350
psi
–CO
L
2
Image 1-35
HA
35120-124
Small
NA
35100-104
Small
RA
35200-204
Small
1000
psi
–CO
L
2
350
psi
– N
L
2
400
psi
Refer
R B
*
*
35205-209
Large
35300-304
Large
400
psi
Refer
350
psi
– N
L
2
**
RB valve bodies are used for both refrigeration and L–N valves. The refer
2
version uses black o-ring plunger guide seals and black faced plungers, while
the
L–N version uses white o-ring plunger guide seals and reddish faced
2
plungers. See the sections on plunger guides and seals and plungers for more
information.
Table 1-1
SB1001.01-15

Decision Tree for Identifying Valve Bodies without Body Stamps
“D” size
What size valve is it?
The smaller valve is a “B”
valve and measures roughly
1¼” (32mm) in diameter and
2³⁄₈” (60mm) tall. The larger
valve is a “D” valve, it measures
roughly 1⁵⁄₈” (41mm)
diameter and almost 3”
(76mm) tall.
“B” size
Image 1-42
“B” size valve - go to Page 17
“D” size valve
Where is the Outlet?
If the outlet is on the
bottom you have a
L–CO 2
valve - If the
Outlet is on the opposite
side of the Inlet you
have a L–N 2
valve.
Image 1-43
Outlet is on the bottom - valve is
a L–CO 2
valve. If your valve has
the Outlet on the bottom and
has a body ID stamp and
wrench flats see Page 15.
Outlet is on the opposite side of
the Inlet - valve is a L–N 2.
Small or large orifice?
The valve on the left has a tiny ³⁄₆₄ orifice, while the
one on the right has a ³⁄₃₂ orifice.
This is an L–N 2
valve Sigma
35305-309 (“D” 225 psi
MOPD L–N 2
valve)
(D2024-S15).
Refer Service note: This
valve was used for refer units
when fitted with black o-ring
plunger guide seal and black
faced plunger.
Image 1-44
The small orifice ³⁄₆₄ valve
is a Sigma 35325-329
(“D” 1000 psi MOPD
L–CO 2
valve)
(D2011-S25).
The large orifice ³⁄₃₂ valve
is a Sigma 35315-319
(“D” 300 psi MOPD L–CO 2
valve) (D2013-S39).
SB1001.01-16

Web
“B” Size valves (con’t from page 19)
Does the Inlet have a
“Web” ?
A web is a small metal
ridge or “web” left when
two holes are drilled
close to each other. The
valve on the right has a
web the one on the left
does not.
Image 1-45
Valve with web
go to on page 18
Valve without web
is a L–CO 2
valve
Does the L–CO 2
valve have a Small (³⁄₆₄) or large (³⁄₃₂) orifice?
The valve on the right has a tiny ³⁄₆₄ orifice, while
the one on the left has a ³⁄₃₂ orifice.
Image 1-46
The large orifice ³⁄₃₂ valve
is a Sigma 35315-319
(“B” 300 psi MOPD L–CO 2
valve) (D2023-S13).
Refer Service note: This
valve was used for refer
units with special plunger
guide sealing. This unit is
not field serviceable, other
than replacement of the
activation coil. Replace
entire valve with newer
refer valve #35200-4
The small orifice ³⁄₆₄ valve
is a Sigma 35125-129 (“B”
1000 psi MOPD L–CO 2
valve) (D2021-S9).
Note: If your valve body has a
body stamp - refer to page 15.
SB1001.01-17

Valve with web
Is body machined for Variseal
or Standard o-ring?
Valves that use standard
o-rings have a slight undercut
at the base of the threads
for expansion of the standard
o-ring when the plunger guide
is tightened. Variseal bodies do
not have this undercut.
No undercut
Undercut
If you attempt to place a standard
o-ring in a Variseal body
the o-ring will not go in (image
1-49 on page 19). If you place
a Variseal o-ring in a standard
body the seal will be loose
(image 1-48, on page 19) and
allow leakage of coolant. See
page 10 for other ways to distinguish
the two body types.
Variseal
Standard O-ring
Location of
undercut
Image 1-47
Valve bodies machined
for Variseal o-ring
Valve bodies machined
for standard o-rings
Variseal o-ring\body
Valve is a Sigma 35105-109 (“B”
175 psi MOPD L–N 2
valve -
going obsolete at the end of
2001.) (A2025-S28)
Current Variseal valves have ID
stamps on the bodies see page
15 for details)
Standard o-ring\body
Valve is a Sigma A2025-S26
or “S26” (small 175 psi MOPD
L–N 2
valve - Obsolete)
Seal notes: Standard o-ring
seals MUST be replaced everytime
a valve is opened.
Note: Removing a Variseal
o-ring is only required every
10-15 servicing, unless the seal
is broken, damaged, or distorted.
SB1001.01-18

Gap
Image 1-48
A Variseal seal in Variseal
body will be centered in the
cavity.
A Variseal seal in standard
o-ring body design will slide
to the bottom of the cavity
and have a gap at the top, if
tilted on its side.
Image 1-49
A standard o-ring will not fit
in a Variseal body, because the
Variseal body lacks the undercut
for the o-ring.
SB1001.01-19

Plungers & Springs
Plungers and springs are sold as service parts as a
set. The plungers for small valves have the spring
integrally attached, so keeping the correct spring with
the plunger is easy. The plunger springs for all large
valves are the same value, so it’s not important to keep
them separated.
Plungers are made in two sizes with any of three face
materials and two finishes (image 1-36).
Image 1-36
L–N 2
and L–CO 2
plungers typically have a black
coating - refer plungers typically do not.
Back two rows show D” plungers and springs
Front row is “B” size plungers with attached springs
Note: Springs are wound to a smaller diameter on one
end than the other. The small end goes near the flanged
face of the plunger.
The face material of the plunger determines the coolant
for which it is best suited. The face will be white for
L–CO 2
, reddish for L–N 2
, or black for refer (Image 1-37).
Some early valves used the white face material for
L–N 2
and refer service. However, for best valve
function, use a plunger with the correct face.
Plunger guides & seals
The distinguishing characteristics of plunger guides are
size and seal type. Three types of plunger guides are
made (Image 1-38):
L–CO 2
L–N 2
Refer
Image 1-37
Small “B” for use with o-ring type seals
Small “B” for use with Variseal type seals
Large “D” for use with o-ring type seals
All “D” plunger guides are interchangeable. They can be
used with any “D” valve body and either white or black
o-ring seals.
Image 1-38
“B” size plunger guides for o-ring
type seals are used in A2025-S26
(obsolete), L–N 2
valves with a
white o-ring and also in Sigma
35200-204 refer valves with a black
o-ring.
“B” for o-ring
type seal
“B” for
Variseal
“D” for o-ring
type seal
“B” size plunger guides for Variseal
type seals are used in all L–CO 2
“B” valves and all L–N 2
“B” valves
except the obsolete A2025-S26.
Image 1-39
SB1001.01-20
“B” with black
o-ring seal
“B” with white
o-ring seal
“B” with
Variseal

Actuating Coils
Valve actuating coils (simply referred to as “coils”
from here on) should have labels that show their
voltage and power (watts). If there is no label
on a coil, discard the coil. While a coil may
function for a time on the wrong voltage, there
is a significant risk that the coil or valve will fail
possibly resulting in a run-away cold condition, or
damage to the temperature chamber or thermal
platform. The risk of using an unknown coil is
much higher than the cost of a new one.
Coils are made in two sizes, “B” (smaller) and
“D” (larger) - (image 1-40). Valves will very closely
match the diameter of the valve body they go
with.
Coils made before late summer of 2001 were
available in 120V, 208V, and 240V - 60 Hz. Note
that 208V coils are not interchangeable with
240V coils. However, 208V-60Hz coils can be
used with 220V-50Hz.
“D” coil
Image 1-40
“B” coil
Coils made beginning late summer 2001 work
with wider voltage ranges in some cases. Check
the coil label for proper voltage.
If a coil is the proper size, voltage, and wattage, it
can be used on any valve that has the matching
power requirement. These are the power ratings
and their appropriate valve matches:
6w
8-9w
L–N 2
“B” valves rated at 175 psi MOPD
A2025-S26
35105-109 (A2025-S28)
L–CO 2
“B” valves rated at 300-350 and
1000 psi MOPD
35115-119 (B2023-S13)
31510-104
35125-129 (B2021-S9)
35120-124
Refer “B” valves rated at 400 psi MOPD
35200-204
L–N 2
“B” valves rated at 350 psi MOPD
35100
L–N 2
“B” valves rated at 175 psi to raise
the valve MOPD rating to 300 psi
A2025-S26
35105-109 (A2025-S28)
10w
13-14w
L–CO 2
“D” valves rated at 300 psi and
1000 psi MOPD
35315-319 (D2013-S39)
D2011-S25
L–N 2
“D” valves rated at 225 psi MOPD
35305-309 (D2024-S15)
L–CO 2
“D” valves rated to 350 psi MOPD
35310-314
L–N 2
“D” valves rated at 350 psi MOPD
35300-304
Refer “D” valves rated at 400 psi MOPD
35205-209
SB1001.01-21

Coils are made in two housing styles, “grommeted” and
“conduit hub” (Image 1-41). The terms refer to the
method of wire lead exit and sealing.
The conduit hub housings are the more modern design
and allow for improved sealing and thus improved coil
life in some applications. The type of housing does
not affect the suitability of a coil for a particular valve.
However, be aware the older grommeted housing coils
will likely have a shorter service life in very wet/cold
conditions.
Image 1-41
Conduit type coil
Grommet type coil
SB1001.01-22

Identifying Valves by Valve Numbers
If you have an intact valve that you are confident has not been modified, and
that has an intact label, use the charts below to determine the valve type.
Valves with Non-Sigma numbers:
N
umber
C
oolan
t
M
OP
D
Statu
s
A2025-S26
A2025-S28
L–
N
175
psi
obsolete
2
L–
N
175
psi
going obsolete end of 2001
2
A2025-S31
L–
N
175 psi
2
same as A2025-S28 except has
mounting bracket on coil housing
B2011-S53
B2013-S47
B2021-S9
L–CO
1000
psi
obsolete - no service parts available
2
L–CO
300
psi
obsolete - no service parts available
2
L–CO
1000
psi
going obsolete end of 2001
2
B2021-S14
L–CO
1000 psi
2
same as B2021-S9 except
bracket on coil housing
has mounting
B2023-S13
L–CO
300
psi
going obsolete end of 2001
2
B2023-S15
L–CO
300 psi
2
same as B2023-S13 except has
mounting bracket on coil housing
D2011-S25
D2013-S39
D2024-S15
L–CO
1000
psi
going obsolete when stocks depleted
2
L–CO
300
psi
going obsolete when stocks depleted
2
L–
N
225
psi
going obsolete when stocks depleted
2
Table 1-2
Valves with Sigma numbers:
Note: Sigma numbers designate both the valve type and the valve voltage. Thus each valve is
designated by a range of numbers such as 35100-104. This means to include 35100, 35101,
35102, 35103, and 35104; all of which are the same valve with coils for differing voltages.
S
igma
Number
C
oolan
t
M
OP
D
Comment
s
35100-104
L–
N2 350
psi
replacement for A2025-S2
35105-109
L–
N2 175
psi
same as A2025-S28
35110-114
L–CO2 350
psi
replacement for B2023-S13
35115-119
L–CO2 300
psi
same as B2023-S13
35120-124
L–CO2 1000
psi
replacement for B2021-S9
35125-129
L–CO2 1000
psi
same as B2021-S9
35200-204
Refer
35205-209
Refer
400
psi
new in summer of 2001
400
psi
new in summer of 2001
35300-304
L–
N2 350
psi
replacement for B2024-S15
35305-309
L–CO2 225
psi
same as B2024-S15
35310-314
L–CO2 350
psi
replacement for B2013-S39
35315-319
L–CO2 300
psi
same as B2013-S39
35325-329
L–CO2 1000
psi
same as B2011-S25
Table 1-3
SB1001.01-23

SIGMA SYSTEMS CORPORATION
Technical Bulletin #SB1003.00
Valve Disassembly and Assembly
3163 Adams Ave
San Diego, CA 92116
619.283.3193
This bulletin covers how to disassemble and
assemble valves used in Sigma chambers and
platforms (plates). The pictures to the right
show an exploded view of a valve and two
samples of typical mounting of valves on the
back of a chambers.
Note: This bulletin shows valves mounted only
in temperature chambers, as thermal platforms
are more compact and harder to photograph.
The procedure for valves is the same whether
they are in a chamber or a platform.
Exploded view of typical valve
Image 2-1
Before beginning with the disassembly of a
valve make sure:
A) That coolant source is turned off and that
the valve has been disconnected from the
coolant source.
B) That electrical power is removed from the
chamber or platform
C) That electrical power is removed from the
controller.
Failure to follow these simple instructions can
result in serious injury and death.
Typical valve assembly on back of chamber with
primary L–N 2
valve on right and a redundant or
safety valve on left
Image 2-2
Extremely
thin walls
During disassembly and assembly of the valve
be careful not to damage or distort the plunger
guide. Its precision walls are very thin and can
easily be damaged.
SB1001.01-24
Typical single valve assembly on back of chamber.
Image 2-3

1. Removing the coil retention nut – You should be
able to loosen the nut by hand (image 2-4). If it is
stuck use a ⁹⁄₁₆” wrench to loosen it.
2. Removing the coil – Remove the coil by sliding it
off the plunger guide stem (image 2-6).
Caution: If resistance is felt when lifting the coil
Do NOT increase force to remove the coil. Use
a small screwdriver to gently lift it loose from the
insulative layer (image 2-5).
Increased pulling of the coil when resistance is
felt can lead to separation of the Flux plate from
the coil (image 2-7). If separation of the Flux
plate occurs you must replace the coil as further
operation of a coil will lead to premature failure.
Note: You can use a coil with a separated Flux
plate for a short period of time until you can obtain
a replacement. To operate a valve with a detached
Flux plate, place the Flux plate in it’s regular position
on the bottom of the coil when reassembling
the valve. This should not affect performance, it
just accelerates failure of the coil, as the coils
moisture seal has been compromised.
Image 2-4
CAUTION: If you use a tool
to pry the coil and flux plate
loose, be VERY gentle so you
don’t bend or distort the very
thin walled plunger guide tube.
Image 2-5
Flux plate intact
Image 2-7
Image 2-6
Flux plate is separated
- requires
replacement of
the coil
SB1001.01-25

3. Removing the insulation layer – This will
be made of either black foam (image 2-8 &
9) or a thermal barrier washer (image 2-10).
Removal of the black foam may require the
use of a sharp knife to cut around the top
(image 2-8) allowing the top to be removed
(image 2-9).
IMPORTANT: Make sure to keep the
washer or insulative foam for replacement.
Failure to put this layer of “insulation” back
can cause the coil to freeze and lock the
valve in an open position causing a free
flow of cryogenic coolant.
Image 2-10
Image 2-8
Image 2-9
SB1001.01-26

4. Removing the plunger guide – Once the
foam or thermal barrier washer is removed, the
base of the plunger guide will be exposed. The
plunger guide will be one of two kinds, either it
will have two opposing detents (image 2-11) for
use with a spanner wrench or Sigma spanner
nut (image 2-12), or it will not.
If your valve does not have spanner holes,
replace the valve. It is a very old A2025-S26
valve that has given all the service expected
of it.
Always use the a proper spanner wrench or
nut that engages the two detents to open the
valve.
Do NOT use a screwdriver or other object
in the slot at the top of the plunger guide
(image 2-14).
That slot is for another purpose. It is very
easy to distort the plunger guide by using the
screwdriver slot to open the valve. Such distortion
can easily lead to valve failure and a “runaway”
cold condition.
NEVER use any type of tool that grips the
stem of the plunger guide. The guide is
hollow, thin, precision machined and easily distorted.
Once distorted, it must be discarded.
Place the spanner nut over the valve guide
as shown in image 2-12, with the pins in the
detents in the plunger guide base, and use a
box end wrench to push down and turn in one
action (image 2-13). If the valve is mounted in
the temperature chamber or thermal platform,
use care to avoid bending mounting brackets,
plumbing, etc.
Sigma
spanner
nut
Detents
Image 2-11
Image 2-13
Image 2-12
Image 2-14
Hint: As you remove the plunger guide it is likely
that the plunger and spring assembly will fall out.
Use care when removing the guide so that the
plunger and spring assembly is not lost.
SB1001.01-27

When you remove the plunger guide you will
now be able to see inside the valve body
(image 2-15).
5. Removing the Seal - Whether or not
removal of the seal is required is dependant
on the type of seal.
White or black o-rings MUST be
replaced each time the valve is opened.
Variseals can be left in place 10-15
times without replacement, unless
broken, damaged, or distorted.
The seals are easily removed using a
finger nail or a smooth non-sharp instrument
(image 2-16) by gently prying under the seal
and lifting it out (images 2-17 & 18).
Note: A smooth edged staple remover like
the one shown in image 2-16 can work as a
seal removal tool.
Image 2-18
Image 2-17
Image 2-16
Image 2-15
SB1001.01-28

To Reassemble the valve.
1. Make sure that the valve body, inlets, and
outlet orifice are clean and free of debris
(image 2-19).
2. If required place the correct seal (white,
black or Variseal) in the base of valve body
(image 2-19).
Note: White and black o-rings must
be replaced every time the valve is
opened. Variseal o-rings need only be
replaced every 10-15 openings, unless
they are broken, damaged, or distorted.
3. Place the plunger and spring assembly in
the plunger guide (image 2-20).
4. Thread the plunger guide into place in the
valve body.
Image 2-19
Note: Take care to be sure that no
insulating foam is caught in the plunger
guide threads.
Then use a spanner wrench or spanner
nut to tighten the plunger guide to a snug
tightness. A snug tightness is what could
be applied using a screwdriver; without the
advantage of the lever provided by the long
wrench handle. Note: Do NOT use a screwdriver
to tighten the plunger guide. The
actual specs are 20 inch lbs for “B” size and
25 inch pounds for “D” size.
Image 2-20
Image 2-21
SB1001.01-29

5. Replace the black insulative foam or thermal
barrier washer, this is very important to prevent
coil freeze up and cold “run aways”
(image 2-22 or 2-24).
Tip: If you have a valve with black foam
between the body and coil it is recommended
that you replace the foam with a
Sigma thermal barrier washer. To do this,
cut the surrounding foam flush with the top
of the valve body (image 2-23). Discard
the black foam and replace it with a Sigma
thermal barrier washer (image 2-24) (part
number 35831 for “B” and 35830 for “D”
valves).
6. Slide the coil onto the plunger guide.
7. Use coil retaining nut to hold the coil in place.
Tighten to snug tightness only (image 2-25).
Excess tightening will compress the insulative
layer and can damage the plunger guide.
Foam under the coil should not be compressed
flat, again we recommend replacement
of the black foam with a Sigma thermal
barrier washer.
Image 2-22
Image 2-23 Image 2-24
END
SB1001.01-30
Image 2-25