Product - PC 50 Pneumatic Control Unit

​​​​​​​​​Pneumatic Control Unit for safety valve control with piston and lifting device


Key Features

The IMI Bopp & Reuther pneumatic control PC 50 is used to control safety valves with
modular differential surface double acting piston types AK or safety valve SiZ 2507 with integrated differential surface piston.

  • Quick response times
  • High setting accuracy (low tolerance)
  • Good repeat accuracy
  • Testing of reliability during operation by integrated test valve group with locking bar
  • No air consumption during working condition

Control of all IMI Bopp & Reuther safety valves

Set pressures
0.1 baržg up to 250 baržg
Modular design
  • Standard device is purely pneumatic
  • Triple redundancy of pressure switches
  • Pressure switches can be checked during operation
  • Only one auxiliary power (pneumatic air) required for operation
  • Only one auxiliary power (pneumatic air) required for operatio

Pressure switch
  • Frictionless force-balance system
  • High setting accuracy of set pressure (<99%)


  • In conjunction with assisted safety valves
  • Power Generation
  • Gases, steam or liquids
  • Chemical Industries
  • Process Industries
  • Petrochemicals
  • For nuclear application the Control Unit PC 50 is available in stainless steel body housing with reinforced superstructure. This design is dynamically qualified for 3g including fundamental frequency test.

Extension options

  • Safety valve testing option
  • Magnetic remote release
  • Electrical heating (with response)
  • Ex-design (explosion proof)
  • Brass and bronze free
  • Pressure transmitter for critical medium​

Approvals and standards

EC type examination
  • Pressure Equipment Directive 97/ 23/ EG
VdTÜV type approval according to 
IMI Bopp & Reuther will not renew the existing VdTÜV type approvals. The requirements by VdTÜV and applicable standards are completely covered by the EC type examination.​

Type code


Control Unit PC 50 - Dimensions

Pneumatic piston AK

The pneumatic actuator AK follows the relief principle and uses differential surface pistons of a “flying piston” design. This ensures frictionless opening as a spring safety valve if the air supply fails. The safety valve will no longer be gastight at the upper end of the bonnet once the actuator is set up. If a gastight design is required (typically for all applications except steam), a bellows design will need to be selected.​

  • Differential surface double acting piston for accurate performance (area of loading piston larger than area of lifting piston).
  • On failure of supply air the control air is vented o the pneumatic system, the piston spring is forcing apart the piston halves and the piston stem is free (flying piston). The valve operates as a springloaded safety valve.
  • Five piston sizes cover all valve dimensions and pressure ranges.
  • The piston integrated locking nut allows for safety valve gagging for e.g. pressure system hydro test.
  • A post installation modification of existing spring loaded safety valves is possible to optimise the functional performance, e.g. in case of increasing operating pressures.
  • The piston assembly AK is an approved optional design for IMI Bopp & Reuther safety valves with TÜV-type test and CE marking.

Lifting valve assembly​ LG 22 and LG 33


  • The lifting valve assembly LG 22 has one loading air inlet and one lifting air inlet, with outlets for two valves’ loading and lifting air. The LGž33 has outlets for three valves’ loading and lifting air.

  • The LG 33 is required for the connection of three safety valves to one PC 50 control unit with easy operation. The LG 22 may be used for two safety valves.

  • The 3/2-way valves built in the lifting valve assembly enable selection of all pneumatic
    system connection mode, i.e. for each valve separate lifting air on/o.

  • Lifting of a single safety valve is possible without change of production function
    of the 2nd or 3rd valve.

  • In case of long pipe runs between the control unit and multiple valves the piping e​​ffect may be reduced with a lifting and loading air manifold within short distance of the safety valves.​

Pneumatic assisted safety valve​

Controlled safety valves are used primarily where standard spring-loaded safety valves cannot meet stringent operating conditions. Typical applications are systems with high operating pressures, increased tightness requirements, limited opening and reseating parameters, critical applications.

Operation of controlled safety valves

In addition to the safety valve spring the controlled safety valve is equipped with an air pressure cylinder piston. After startup of the control unit the loading air is built up above the piston. The space below the piston can be operated either with continuously present lifting air or without lifting air. The control unit PC 50 operates in accordance with the closed circuit principle, i.e. the loading air discharges by reaching the engage pressure (usually set pressure). The pressure switches work as redundant multiple monitoring (e.g. 3 control lines in a 1 out of 3 principle). Once triggered, the loading air is released thus removing the additional closing force and the safety valve opens supported by the lifting air present below the piston or without lifting air and as a spring loaded safety valve with its own opening characteristics. In case of air supply failure controlled safety valves operate exactly like direct spring loaded safety valves. The control unit PC 50 and the controlled safety valves fully meet the requirements according to DIN EN ISO 4126-5, AD 2000-A2 and TRD 421.​

Benefits of controlled safety valves

  • Improvement of the static performance, e.g. increased tightness up to valve opening, high setting accuracy, and precise repetition of the set pressure thus improving operating efficiency.
  • Improvement of the dynamic performance, e.g. reduction of the opening and reseating hysteresis, stabilisation of the valve blow-o, controlled safety valve opening below the set pressure, controlled overflow with pressure maintenance improving operating efficiency and reducing down time.
  • Minimal accumulation and blowdown
  • High tightness of the safety valve up to set-pressure
  • Stabilised function of the safety valve
  • Requirements in high operating pressure or the size of the safety valve, may require the use of controlled safety valves while still guaranteeing operational safety.
  • With the use of the control unit, the operating pressures can be staggered in multiple valve applications increasing the level of control on the system and avoiding unnecessary loss of medium.


  • In conjunction with assisted safety valves Power Generation
  • Power Generation
  • Gases, steam or liquids
  • Chemical Industries
  • Process Industries
  • Petrochemicals
  • For nuclear application the Control Unit PC 50 is available in stainless steel body housing with reinforced superstructure. This design is dynamically qualified for3g including fundamental frequency test.​

Flow diagram PC 50 in operating position with one safety valve​

Steam generator application

Example of a steam generator application​

In the above application two controlled safety valves are installed on the drum and one controlled safety valve on the superheater. The set pressure of the superheater safety valve is lower compared to the drum safety valve and is in operation with lifting air on (connection mode N, see type code page 3).

In order to ensure that no condensate will flow back to the main pressure system line the control unit must be placed at a lower elevation than the main steam pipe.

Pressure tapping lines are typically located on the higher elevation of the pressure system, offset to each other and water seals are to be used when utilizing hot mediums. The pressure tapping lines shall be installed in horizontal direction or downwards to the steam pipe. The vertical upward tapping line part is always hot and has condensate return which drips in the steam pipe. These hot segments of the pressure tapping lines have to be insulated. 

For detailed installation instructions please see operating and maintenance manual.

The connection mode of the drum valves is arrangement T (see type code page 3), i.e. loading air only. The pressure tapping lines are connected to the drum and the superheater. In case the steam system pressure triggers the set pressure of any pressure switch (1 out of 3), the loading air is vented from safety valve cylinders. The superheater safety valve opens first supported by the lifting air, while the drum safety valves are still closed due to higher spring setting.

The sole opening of the superheater safety valve covers many relief cases with short pressure increase and cooling of the steam generation system is further ensured, because steam is relieved at the system end. 

Should the pressure in the steam generator increase further, the drum safety valves open against spring setting and the total generated steam capacity is discharged​ to retain safe pressure levels.

Mobile Testing

Test of the Set Pressure of the Safety Valve during Operation

One of most important benefits of the mobile testing is that the set pressure of a safety valve can be tested during operation.

The registered lifting air pressure PH1 and PH2 at the pressure gauge and the pressure of the system are entered into a diagram.

The test procedure is carried out at first (zero point method) with two system pressures at least- in the diagram the points 1 and 2.

The connecting straight line through the measured points meets the x-Axis of the diagram at the set pressure.

If, during a repeated test, the measured values are on the characteristic line of the zero point measurement, this is considered as a proof of the set pressure.​

Latest News

Valve Doctor programme celebrates 20th anniversary
16 September 2019
Unconventional support for the unconventional oil and gas industry
01 July 2019
17 June 2019
IMI CCI showcases choke valve at DUG Rockies conference
04 June 2019
Jackie Hu appointed Divisional Managing Director of IMI Critical Engineering
07 March 2019
Roy Twite to succeed Mark Selway as Chief Executive of IMI plc
05 March 2019
IMI Critical holds Safety Summit
21 September 2018
New HSE handbook to help keep field service engineers safe
10 August 2018
Safety first at IMI Critical
31 July 2018
IMI InterAtiva’s Series RK Valves certified ‘fire-safe’
24 July 2018
IMI CCI participates at regional VPP Safety Summit
08 June 2018
Largest Romanian customer recommends IMI Remosa
10 May 2018
Lean success in IMI Critical back office functions
04 May 2018
Isolation valves adapted for Fluidised Catalytic Cracking applications
30 April 2018
IMI Critical Korea closes in on world-class LEAN performance
27 April 2018
IMI board tours IMI Critical businesses
25 April 2018
New positioner software tools from IMI STI
08 February 2018
Launch of Zero Backlash Scotch Yoke Mechanism
16 January 2018
IMI Critical Korea certified to sell actuators in Europe
20 September 2017
IMI Critical named ‘supplier of the year’ by Korea’s Doosan
19 September 2017
100th Valve Doctor graduates from IMI Critical
13 September 2017
Top HSE certification for IMI Critical’s California site
12 September 2017
Launch of High Endurance Actuator
21 April 2017
Launch of AB6350 valve
06 April 2017
Launch of 100DPC Multi-trim
17 March 2017
Launch of 840GS control valve
22 December 2016
IMI Critical to exhibit new technology at ADIPEC 2016
25 October 2016
New graduates join IMI Critical in four countries
22 September 2016
IMI Critical to take stand at ONS 2016 in Norway
16 August 2016
IMI Critical opens new China plant in Qingpu
27 July 2016
IMI CCI Korea celebrates 2,000 days of no “Lost Time Accident”
25 July 2016
Visit to IMI Z&J Germany by the Russian Economic Bureau from Bonn
11 July 2016
IMI Z&J Düren moves into modern offices
08 July 2016
IMI Critical Engineering forms strategic partnership with MRC Solberg & Andersen
05 April 2016
IMI Way Day 2016 date announced
01 March 2016
NEW IMI Eye – fourth edition
26 February 2016
IMI Critical co-locates China businesses
20 January 2016
IMI CCI Switzerland gains certification for new generation safety valves
18 December 2015
IMI Critical rise to Dragon challenge
30 November 2015
IMI STI achieves CRCC approval for new products
24 November 2015
IMI Truflo Marine Attend the Engineering Technology and Innovation Exhibition 2015
23 November 2015
IMI CCI Sweden secures new contracts on three continents
23 November 2015
IMI Critical Engineering appoints new petrochemicals head
05 November 2015
IMI CCI Czech Republic gains ‘Safe Enterprise’ certification
03 November 2015
IMI Critical announces 90mRMB investment in China
29 October 2015
IMI CCI SriCity wins regional safety award
27 October 2015
Key clients attend grand opening of new Aberdeen facility
23 October 2015
IMI companies ‘act as one’ to deliver for customer
02 October 2015
IMI CCI Sri City approved by NTPC
01 October 2015
IMI Critical Engineering showcases innovation at Valve World Expo Asia
28 September 2015
Nexen awards IMI Orton
25 September 2015
IMI Critical Engineering celebrates opening of new Jubail repair centre
23 September 2015
IMI Critical and IMI Precision join forces at Valve World Expo + Conference Asia 2015
21 September 2015
IMI Critical Engineering opening of new Jubail Repair Centre
18 September 2015
IMI CCI India manufactures first 1050MW turbine bypass valve
20 May 2015
Largest ever contract for IMI Critical Engineering
18 February 2015
New Houston facility opens
12 February 2015
IMI Critical completes acquisition of Bopp + Reuther
02 January 2015
IMI Critical takes family of brands to Valve World 2014
11 December 2014
IMI STI doubles size of Italian plant
20 October 2014
Product - PC 50 Pneumatic Control Unit