Model 754 Rate Of Flow Control (N.o.) - Emerson Daniel 700 Series Technical Manual

Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013

Model 754 Rate of Flow Control (N.O.)

Closes on increasing differential pressure
A rate of flow or flow limiting valve is normally open and throttles toward a closed position on increasing differential pressure (P4
minus P1). It is a regulating or positioning type valve that does not require any outside power source to operate.
The pilot control is normally open. It is an adjustable spring loaded variable orifice in the Z-port. The pilot is piston operated,
spring biased (loaded) with a differential pressure sensing chamber connected to two separate pressure sources.
Rate of flow valves are used for:
1. Limiting the maximum flow through meters.
2. Limiting the maximum flow through pumps, process streams, etc.
FULL OPEN - NO CONTROL - The pilot is full open. Differential pressure (P4 minus P1) is less than
the pilot spring setting. Y-port (P3) is open to Z-port (P2). The valve is floating the stream and is
not required to control.
P4
= Inlet Pressure
= Outlet Pressure
= Product Pressure
Sense Line (Hi)
Flow Meter
Note: Minimum of 5 psid required for Control
Sense Line (Lo)
Needle Valve/Strainer
(Closing/Sensitivity Control)
P3
X
P1
Figure 4-20
28
Differential
Pilot (N.O.)
Y
Z
P2