Pressure Independent Combi Valves (PICV)

For rooms, zones, ventilation and air-conditioning systems

  • Integrated differential pressure controller
  • Valve body made of dezincification resistant hot-pressed brass (DZR)
  • Volumetric flow 30…1800 l/h
  • Differential pressure range 17…600 kPa
  • Internally threaded Rp conforming to ISO 7-1
  • Externally threaded G conforming to ISO 228-1
  • Version with pressure test points for Δp measurement (optional)
  • Can be equipped with electrothermal or electromotive actuators
    – STA..3.. (2-position)
    – SUE21P (2-position)


  • In ventilation and air conditioning plants for control on the water side and automatic hydraulic balancing of terminal units, such as fan coils, induction units, and in heat exchangers for heating and cooling, with 2-point control
  • In heating zones, such as self-contained heating systems, apartments, individual rooms, etc.
  • For closed circuits

Technical design

  1. Ring with dial for presetting
  2. Variable presetting opening
  3. Differential pressure controller
  4. Flow control valve
  5. On/Off control valve
  6. Pressure test point, blue ribbon, P-
  7. 7 Pressure test point, red ribbon, P+

A Inlet port A
B Outlet port B

PICV VQ..46..Q (shown here) is additionally equipped with pressure test points P/T.

Functional principle

The above drawing is used as a reference for this following description. The medium entering the valve (inlet port A) passes through the variable presetting opening [2] which is connected to the ring with the dial [1] for presetting the desired maximum volumetric flow. Then, the medium flows through the On/Off control valve [5].

The actuator opens and closes the On/Off control valve [5]. After the presetting, the medium passes through a built-in mechanical differential pressure controller [3]. This differential pressure controller is the heart of the PICV and ensures that the selected volumetric flow is maintained across the whole working range and independent of the inlet pressure P1.

The PICV VQ..46..Q are additionally equipped with 2 pressure test points (P+, P-). These pressure test points allow the measurement of the differential pressure across the PICV in order to check if the Δp is sufficient to reach Δpmin. For that purpose, the electronic manometer ALE10 can be used.

P1  Pressure at inlet of PICV
P2  Pressure at outlet of presetting
P3  Pressure at outlet of PICV
P+  P/T port, pressure test point with red ribbon [7]
P-  P/T port, pressure test point with blue ribbon [6]

A  Inlet medium (inlet port)
B  Outlet medium (outlet port)
2  Ring with dial for presetting
4  Differential pressure controller maintains the
pressure P1 – P2 constant across the presetting [5]
6  On/Off control valve with mounted actuator

Manual control

The manual control knob can be fitted to protect the valve stem and facilitates manual control of the PICV during commissioning. The manual control knob is delivered loose in the box.

Factory setting:

The valve is open. To close the valve, turn the manual knob clockwise.
The valve must be open to purge the system.


Engineering example

Basis of calculation

  1. Determine energy demand Q [kW]
  2. Determine temperature differential (supply – return) ΔT [K]
  3. Calculate volumetric flow

    Hint: you can also determine the volumetric flow using the valve slide rule.
  4. Select suitable PICV
    – Pipe connections (internally or externally threaded)
    – With or without P/T ports
    – Ideally, PICVs should be selected such that they operate at about 80 % of their maximum flow, enabling them to deliver spare capacity, if required.
  5. Determine dial setting using volumetric flow/dial presetting table, cf. Volumetric flow/dial
    presetting [➙ 4]


Given is a heat exchanger with:

  1. Energy demand: Q = 1.9 kW
  2. Temperature differential: ΔT = 6 K
  3. The valve shall have connections with external threads to ISO 228-1 and size DN 15.
    – PICV selection:
    VQP46.15L0.5 (externally threaded connections, no pressure test points P/T, nominal volumetric flow 520 l/h)
  4. Volumetric flow: 270 l/h
    Dial setting: 2.6

Volumetric flow/dial presetting

Tables to determine the dial setting for a desired volumetric flow.
Δpmin [kPa] based on volumetric flow; interpolate missing values.

Presetting tables indicate expected nominal volumetric flow
During commissioning, check whether current pre-settings correspond to planned design.
● Further adjustment of pre-settings may be required to achieve needed volumetric flow.

Using a linear interpolation will cause a minor offset.

Valve characteristic
Since the VQP/VQI is an On/Off PICV, the valve characteristic is not based on a modulating function. The valve characteristic is made up of two operating points:

  • The PICV is closed at stroke H/H100 = 0 and volumetric flow V/V100 = 0
  • The PICV is open at stroke H/H100 = 1 and volumetric flow V/V100 = 1

Type summary

PICVs, actuators and accessories are packaged and supplied separately.



Ordering (example)

Equipment combinations


NC = Normally closed = VQP46..VQI46.. powerless closed
NO = Normally open = VQP46..VQI46.. powerless open
The valve is fully opened without an actuator


1) Connecting thread pipe side: Internally threaded
2) Usable up to maximum medium temperature of 100 °C

Product documentation

Related documents such as environmental declarations, CE declarations, etc., can be downloaded at the following Internet address:

Technical data

1) Valves where PS x DN < 1000 do not require special testing and cannot carry the CE label.
2) The documents can be downloaded at


National safety regulations
Failure to comply with national safety regulations may result in personal injury and property damage.
● Observe national provisions and comply with the appropriate safety regulations.


The direction of flow indicated by the arrow on the valve body is mandatory!

The valves should preferably be mounted in the return pipe where temperatures are lower and where the sealing gland is less affected by strain.


A strainer or dirt trap should be fitted upstream of the valve to enhance reliability. Remove dirt welding beads, etc. from valves and pipes.
Do not insulate the actuator bracket, as air circulation must be ensured!


Presetting can be done with or without the actuator mounted.


PICV and actuator can be straightforwardly assembled on site. Special tools or adjustments are not required. Prior to mounting the actuator, the required volumetric flow must be set.
The valve is supplied complete with Mounting Instructions (A6V11878322).

Mounting positions

Thermal actuators STA.. may be installed in any position.
Actuator SUE21P must be installed horizontally up to 90° and not hanging


Strong pressure impacts can damage closed PICVs.
- The PICVs must be commissioned with the manual control knob or actuator correctly fitted.
- The PICVs must be open when flushing or pressure testing the system. Flush only on correct flow direction.
- Differential pressure Δpmax across the valves’s control path is not allowed to exceed 600 kPa Strong pressure impacts can damage closed PICVs.
- The PICVs must be commissioned with the manual control knob or actuator correctly fitted.
- The PICVs must be open when flushing or pressure testing the system. Flush only on correct flow direction.
- Differential pressure Δpmax across the valves’s control path is not allowed to exceed 600 kPa

Manual control
When turning the manual control knob in counterclockwise direction or manually operating the actuator, the valve opens. The actuator closes the valve. The valves are supplied fully
open. The manual knob is not designed for permanent manual operation.


The VQP/VQI46.. PICVs are maintenance-free without differential pressure regulator.
Valve plug stem, presetting, diaphragm etc. may not be disassembled.

CAUTION When performing service work on the valve and/or actuator:-
– Switch off the pump and disconnect power supply.
– Close the shut-off valves in the piping network.
– Fully reduce pressure in the piping network and allow the pipes to cool down completely.

Differential pressure regulator cleaning
General notes
The valve insert with the differential pressure regulator can be removed for replacement or cleaning. The removal of the valve from the pipeline is not necessary for this operation. For the cleaning process of the differential pressure regulator, a special tool is needed (ALP54, see Accessories [➙ 6]).

Sealing gland
The stem sealing gland cannot be exchanged. Should leakage occur, the whole valve must be replaced.


WARNING Tensioned return spring
– Opening the valve housing can release the highly tensioned return spring, which can cause flying parts and injuries.
– Do not open the valve housing.

  • The valve should not be disposed of as domestic garbage. Special treatment for individual components may be required by law or make ecological sense.
  • Comply with all local and currently applicable laws and regulations.


Technical data on specific applications are valid only together with Siemens products listed under “Equipment combinations”. Siemens rejects any and all warranties in the event that third-party products are used.

Technical data

1) Valves where PS x DN < 1000 do not require special testing and cannot carry the CE label.
2) The documents can be downloaded at

Application examples

PICVs in HVAC systems combined with variable speed pumps provide even higher energy efficiency. When sizing the pump, it must be made certain that the most critical branch or consumer in the system – usually the most remote from the pump – receives enough pressure (pump head). Thus, it is recommended to use a variable speed pump in constantpressure mode with end-point feedback, to maintain a minimum differential pressure across the critical valve.

Residential buildings
Residential buildings with, for example, self-contained flat heating systems:

E = Floor
G = Group or zone

Non-Residential buildings
Commercial buildings with, for example, fan coil units or heat exchangers for heating or cooling:


1) On valve side: cylindrical thread to ISO 228-1
On pipe side: cylindrical thread to ISO 7-1
2) Maximum medium temperature 100 °C

Revision numbers