Relays - Siemens
Series 62 constant-differential relay
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 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.
Series 63 Constant Differential Flow Controller
The 63 Controller is used in conjunction with an external needle valve to provide constant volume flow rates for either liquids or gases over a continuously adjustable flow range.
In gas service, the 63D is used when the downstream pressure is constant to provide a constant mass flow rate (i.e. standard volume units per time unit; e.g. SCFM). In gas systems where the upstream pressure is constant, a 63U is used.
Constant downstream pressure is not needed for constant volume flow rates (i.e. volume units per time unit; e.g. CFM). Since liquids are incompressible, if the volume is held constant, then the mass is constant.
The 63 Controller is used in conjunction with an external needle valve to provide constant volume flow rates for either liquids or gases over a continuously adjustable flow range.
In gas service, the 63D is used when the downstream pressure is constant to provide a constant mass flow rate (i.e. standard volume units per time unit; e.g. SCFM). In gas systems where the upstream pressure is constant, a 63U is used.
Constant downstream pressure is not needed for constant volume flow rates (i.e. volume units per time unit; e.g. CFM). Since liquids are incompressible, if the volume is held constant, then the mass is constant.