Identifying Valves Used in Sigma Products (SB1001.01)

“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