Pressure Independent Valves Overview

One of problems associated with 2 port control is sizing is making sure all of the control valves have adequate authority. Whilst this problem is helped by the use of differential pressure controllers it can still be difficult to maintain good authorities without specifying that each individual terminal unit require a DPCV. Using traditional valves this would be a very expensive design approach.

The pressure independent control valve (PICV) combines the functions of a differential pressure controller, regulation valve, and 2 port control valve into a single body.

The Pressure Independent Control Valve (PICV) incorporates a small diaphragm type DPCV in order to keep a constant differential pressure across an orifice in order to provide a constant flow rate whilst the differential pressure is with the operating limits of the valve. Beyond these working pressures the valve acts in a similar way to a fixed orifice valve.

The orifice in this case is formed either by the free area between a full port ball and characterising disc or by a globe valve and secondary presetting seat. In both cases the PICV keeps both a constant maximum flow rate regardless of pressure differential and offers motorised temperature control.

Marflow Hydronics currently supply 3 types of pressure independent valve into projects in sizes ranging from DN15 to DN150.

Pressure independent control valve can be used in any hydronic system where there is a requirement to control the flow rate of the heating or cooling media.

Pressure independent control valves are suitable for use in variable and constant temperature systems and may be used as constant flow limiter in constant volume systems (without an actuator head) or as a true PICV in variable volume systems.

Typical applications of the PICV’s may include:

  • Fan Coils
  • Chilled Beams (Active and Passive)
  • Radiant Panels and Radiators
  • Heater Batteries
  • Small Air Handling units
  • Heat Recovery Units
  • Over-door Heaters

Pressure Independent Control Valves are dynamic balancing valves and as such have no requirement for sub-mains and branch balancing valve or differential pressure controllers. As such in most applications the only valves required to balance and control the hydronic circuit are the PICVs at each terminal unit.

Reference Terminal Unit Schematics

Flow Mounted, Variable Volume System with local flow measurement

Return Mounted, Variable Volume System

Return Mounted, Constant Volume System

Features

  • Suitable for many applications.
  • Precision flow control and easy setting.
  • The flow rate is adjustable at local terminals without requiring full system rebalancing.
  • Full stroke equal percentage temperature control valve gives maximum control under all flow conditions.

Benefits

  • Reduces capital outlay by eliminating the need for terminal balancing valves, temperature control valves, branch and mains balancing valves, and system differential pressure control valves.
  • Selection is simple as no authority calculations are needed.
  • Late design changes and changes of use are more easily accommodated.
  • Eliminates most circuit interactivity.
  • Commissioning is simplified as no costly balancing procedures are required.
  • Controllability is made easy due to the equal percentage characteristic.
  • User comfort maximised by ensuring every temperature control valve has full authority.