The Constant Differential Relay maintains a constant pressure drop across an internal needle valve for any flow setting up to about 2.1 cubic feet of air per hour. It thus provides a means for maintaining a practically constant volumetric rate of flow regardless of variations of the process or supply pressures. The differential maintained across the needle valve is 1 to 2 psig. This permits a greater opening of the needle valve, thus making it less subject to clogging. The constant differential relay may be used in conjunction with a rotameter type indicator.
The differential applied to the internal needle valve is determined by a spring-loaded diaphragm in the constant differential relay. This diaphragm controls the action of a valve plunger to automatically admit supply air to the needle valve at the required rate. A self-contained automatic bleed discharges excess supply air to the atmosphere when necessary. The constant differential relay is made of aluminum, brass, stainless steel, Neoprene and Buna-N. The rotameter is constructed of aluminum, stainless steel, borosilicate glass, Buna-N (O-rings), ruby sapphire (float) and brass (fittings). Neither will be affected by ordinary air line impurities.
- With Built-In Needle Valve
- Attached Rotameter Piped Assembly
- Supply Pressure:
Ambient Temperature Limits: -40° to +180°F (-40° to +82°C)
- Minimum: At least 5 psig greater than the maximum downstream pressure.
- Maximum: 150 psig
- Purge Rates:
- Maximum: 2.1 SCFH, 991 SCCM
- Minimum: 0.9 SCFH, 425 SCCM