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Valves & Actuation

Manual Plastic Valves

Constant Flow Valves (1/2" - 4")

Automatic flow control valve that can be manually set for different flow rates. The valve adapts to changing line pressure to maintain a steady flow rate in the downstream piping (see "Principles of Operation") without automation (neither electricity nor an air supply is required). These are not recommended for use with viscous fluids, fluids with high specific gravities, or fluids that contain debris or suspended solids. Accurate to +/- 6% of desired flow rate, and can be adjusted without removing the valve from a line.


Data Sheet


Ideal Applications Include:

Chemical processing, aquariums, mining, water treatment, swimming pools, salt water, semiconductor



1/2", 3/4", 1", 2", 3", 4"










Stainless Steel 304 with PCTFE Coating


30 – 120º F


All wetted parts are of thermoplastic and elastomeric materials for superior corrosion resistance, vertical or horizontal installations, hand wheel permits ON/OFF opening and closing and allows for flow rate adjustment without shutting down the pipeline, springs of Stainless Steel 304 with PCTFE coating tested for long life cycle, prescribed flow setting is clearly visible on the indicator at the top.

  • When the upstream fluid pressure, P1, is introduced at the flow control orifice, it exerts a responding pressure on the upper surface of the flange on the piston type valve plug.
  • Likewise, the downstream pressure, P2, exerts a corresponding pressure to the lower surface of the valve plug flange.
  • Thus, when a differential exists between the fluid upstream and downstream of the orifice, the corresponding differential pressure acting on the surfaces of the flange moves the valve plug piston either downward against the force of the spring cartridge or upward by the force of the spring, depending upon the direction of the force induced by the existing differential pressure.
  • The upward or downward movement of the valve plug piston causes the flow orifice to the widened or narrowed accordingly, thus the flow rate of the fluid passing across the orifice is automatically adjusted. For example, if the differential pressure (P1 – P2) created between the upstream and downstream sides of the orifice increases, the valve plug piston moves downward to narrow the area of the orifice opening and automatically adjusts to the present flow rate value. The reverse is also true when the differential pressure decreases, piston moves upward increasing the orifice opening area and allowing the fluid rate to increase to the preset value.