Identifying Valves Used in Sigma Products (SB1001.01)

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.