Section 4 - 700 Series Valves; Typical 700 Series Valve - Emerson Daniel 700 Series Technical Manual

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

Typical 700 Series Valve

This is the starting point for unlimited control applications. The basic valve now incorporates a pilot control loop, which is
mandatory for it to function.
The basic valve operates on a balanced piston principle, spring biased (loaded). The term balanced piston means that the
exposed area on the spring side (P3) of the piston and the bottom side (P1) are equal in area. The spring is the differential force
that closes the piston when (P1) and (P3) pressures are equal.
By design, the valve serves as a check valve because there can be no reverse flow. It is possible, in some applications, to reverse
flow through the pilot control loop, but this can be eliminated by installing a check valve in the X-port. To open the valve, the
pressure against the bottom of the piston (P1) must exceed the pressure on the spring side of the piston (P3) plus spring force.
CLOSED POSITION - Pilot is closed. Y-port (P3) to Z-port (P2) is closed. X-port (P1) and Y-port (P3)
pressures are balanced. The differential force created by the main valve spring, closes the piston
and keeps it seated.
Therefore, total pressure equals 40 psi @ (P1) and 45 psi @ (P3) or (P3 minus P1) - 5 psid.
The needle valve incorporated with the strainer controls the speed of the closure by controlling the
flow through the X-port.
= Inlet Pressure
= Outlet Pressure
700 SERIES VALVES
Needle Valve/Strainer
X
P1
Section 4
Y
P3
Z
P2
Figure 4-1
14
Manual Pilot Control