Pressure independent control valves

Test Method for PICVs and DPCVs (BTS 1/2019), published by BSRIA in November 2019, defines a pressure independent control valve (PICV) as: ‘A valve that operates to maintain a controlled flow rate that is, within limits, independent of the supplied differential pressure. The valve may operate mechanically or electronically.’

The Illustrated Guide to Mechanical Building Services, Third Edition (BG 31/2017), by David Bleicher, published by BSRIA in 2017, suggests that pressure independent control valves (PICVs) are: ‘…used in variable flow heating or cooling systems to control the output of devices such as air handling units, fan coil units or chilled beams. They regulate flow constantly during varying pressure conditions and can be placed on either the flow or the return pipe.’

Test Method for Heat Interface Units (BTS 2/2015), written by Colin Judd, and published by BSRIA in December 2015 and amended in June 2016, states: ‘A pressure independent control valve (PICV) operates to maintain a controlled flow rate that is, within limits, independent of the supplied differential pressure. A PICV combines the functions of a DPCV, regulating valve and control valve.’

Energy Efficient Pumping Systems, a design guide (BG 12/2011), written by Chris Parsloe and published by BSRIA in 2011, states: ‘Sometimes referred to as a combination valve, a PICV combines the functions of a double regulating valve, differential pressure control valve and two-port control valve within a single valve body. Because the integral differential pressure control valve holds the pressure differential constant across the integral two-port control valve, the flow rate through the valve always returns to its set value whenever the control valve is fully open (since a constant pressure differential across a fixed resistance results in a constant flow rate). The opening through the two-port control valve can be varied manually, and can therefore be used to regulate the flow rate through the valve to the required design value. The flow rate can be set using an integral mechanism within the valve. Once set, the valve will perform the function of a constant flow regulator whenever the two-port control valve is fully open. Only when the control valve begins to close will the flow rate change from its set value.’

Selection of Control Valves in Variable Flow Systems (BG 51/2014) written by Chris Parsloe and published by BSRIA in June 2014, defines a pressure independent control valve (PICV) as: ‘A combination of an actuated two port control valve that varies the flow through a terminal device, and a differential pressure regulator that maintains a constant pressure differential across the control valve thereby ensuring that the set maximum design flow rate cannot be exceeded… Note 4: Although the majority of PICVs are of the type described above, the same objective of pressure independent control can be achieved by a combined two-port control valve and electronic flow measurement device. For products based on this approach, the control valve is fitted with an intelligent motorised actuator that enables the measured flow to be maintained at its required value regardless of pressure variations in the system. This type of valve is sometimes referred to as an “electronic PICV” and does not require an integral differential pressure controller.’

It suggests that typical applications include; modulating control of heating or cooling outputs from air handling units, fan coil units or chilled beams in variable flow systems. (Used without an actuator, PICVs hold flow rate constant at a fixed value regardless of changes in system pressures.)

For more information see: What makes a good PICV?

--BSRIA

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