Emerson Daniel 700 Series - Model 762, 763, 765, 766 and 767 Gas Loaded Pressure Relief;Back Pressure Control Valves

Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013
Model 762, 763, 764, 765, 766 and 767 Gas Loaded Pressure Relief / Back Pressure Control Valves (N.C.) Open on
increasing inlet pressure
These valves are normally closed and open upon increasing inlet pressure. They are used to relieve excess surge pressures
that may occur during a pipeline upset and can also be used to maintain a minimum back pressure for more efcient operating
conditions. These valves are direct acting and do not utilize pilots to operate. They incorporate an integral oil reservoir mounted
on the external surface of the valve cylinder head, which upon installation is partially lled with a light oil. Gas under pressure is
applied to the reservoir. The oil is a moveable barrier between the gas and the valve piston.
Principle of Operation
The valve is normally closed and opens upon increasing inlet pressure. Pressure applied to the nose of the piston is equally
transmitted to the spring side of the piston. When the line pressure on the nose of the piston exceeds the gas pressure, the
moveable barrier of oil compresses the gas and the valve opens.
As line pressure falls below the set point, the gas pressure, added to the spring pressure closes the valve and it remains closed
as long as gas pressure is higher than line pressure. Opening and closing speeds are controlled by a check valve mounted to the
internal surface of the cylinder head. Opening speed is relatively unrestricted which results in very fast opening response. Closing
speed is controlled by a xed orice in the check valve.
Typical Applications
A) Pipeline Pressure and Surge Relief (models 765, 766, 767)
Product movement by pipeline requires over-pressure protection. Response time to pressure rise is critical. These valves will
respond very quickly and only relieve the necessary volume of liquid to decrease pipeline pressure back to or below set-point.
B) Back Pressure Control (models 762, 763)
These valves are ideally suited for back pressure control and minimum pressure drop. When line pressure exceeds the gas
pressure, the valve will open and follow the CV curve for pressure loss.
26