Model 760 Back Pressure/761 Pressure Relief Control (N.c.) - Emerson Daniel 700 Series Technical Manual

Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013
Model 760 Back Pressure/Pressure Relief Control (N.C.)
Opens on increasing inlet pressure
A back pressure/pressure relief valve is normally closed and throttles open on increasing inlet pressure. This valve is used to
maintain minimum pressure for more efficient operating conditions or to relieve excess pressure. It is a regulating or positioning
type valve that does not require any outside power source to operate.
The pilot control is normally closed. It is an adjustable spring loaded variable orifice in the Z-port. The pilot is piston operated,
spring biased (loaded) with a pressure sensing chamber connected to upstream (P1).
Back pressure/pressure relief valves are used for:
1. Back pressure against a pump, meter, hill pressure, etc.
2. Pressure relief and surge control
CLOSED POSITION - The pilot is closed. Inlet pressure (P1) is less than the pilot spring setting,
indicating the main line upstream (P1) is closed, or pressure is not sufficient to overcome the pilot spring
setting. Pilot is closed. Y-port (P3) to Z-port (P2) is closed. X-port (P-1) and Y-port (P3) pressures are
balanced. The main valve spring, being the differential force, closes the valve and keeps the piston seated.
Sensing Chamber Line
= Inlet Pressure
= Outlet Pressure
= Pilot Spring Force
Needle Valve/Strainer
(Closing/Sensitivity Control)
X
P1
Y
P3
Z
Figure 4-9
20
Back Pressure Pilot (N.C.)
P2