Part Number:
2A33687
Release Date:
8/27/2015
Revision: B
8
General Description of Relief Valve Operation:
The SPM
®
EXL Back Pressure Relief Valve’s operation is a simple balance between the nitrogen acting on the
piston and the inlet liquid pressure acting on the rod and wear sleeve. The equation is Pressure times Area
equals Force (PxA=F). The ratio of areas is approximately 25:1 for the 15,000 psi rated valve.
This means that nitrogen pressure of 100 psi can counter an inlet line pressure of 2500 psi for the 15,000 psi
rated Back Pressure Relief Valve. Variations in this ratio in practice are due to friction of seals and will be
discussed in setting and adjusting section on page 11.
End Connection Options:
The SPM
®
3” EXL Back Pressure Relief Valve is available with SPM
®
wing union connections. The nameplate
will indicate the cold working pressure allowable for each assembly.
Wing union connections on the relief valve are interchangeable with other union connections of the same size
and figure (pressure rating). Caution must be taken to avoid mixing different ratings of wing connections.
There are various sizes and figures that are capable of making marginal connections. Failure to observe good
judgment may lead to failure of components and danger to life and limb. Always verify working pressure ratings
of each connection before use.
This device is intended to discharge to atmospheric pressure when it relieves. It must not be subjected to any
significant backpressure; other than that generated by gravity or frictional losses on the discharge line. The
choice of discharge connections is offered as a convenience for the user and does not imply high-pressure
capability.
WARNING: OBSERVE ALL INSTRUCTIONS, CAUTIONS AND WARNINGS AS NOTED IN THIS
MANUAL. FAILURE TO DO SO CAN LEAD TO EQUIPMENT DAMAGE AND PERSONAL INJURY OR
DEATH!
