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

Usage
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%)





Applications


  • 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 
TÜV.SV.1053
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

​Assembly


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​

Features
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.

Applications

  • 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.​


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Product - PC 50 Pneumatic Control Unit