Zetkama Safety Valve Fig 570
Principle of operation
The purpose of the safety valve is to protect the equipment and installation against excessive pressure above the pressure limit. When the force coming from the pressure acting on the disc surmount with the weight of the working elements, the valve starts to open. A further increase in the pressure, required for the particular design of the valve, causes its full opening aided by the bell
2. Delivery condition
Supplied valves are tested and set for the required opening pressure. Valves are stamped on a nameplate fixed to the body and with the of signs on the edge of the outlet flange.
Set pressure is secured by sealing between the cap and bonnet. In order to secure the valve during transport, the lever is being attached to the outlet flange with a wire, and the flow holes are being plugged. For transportation the spindle is secured with a blocking screw, fastened with a metal strip. The external surfaces of the valve are painted.
3. Installation of safety valves
- Before the installation on the unit or pipeline, remove the fastening tape, take out the blocking screw, unscrew the plug and check if valve was not damaged or contaminated during transport. It is absolutely necessary to check the cleanliness of flow channels, external surfaces and end connections. Surfaces of flanges should be cleaned of preservative and of any possible impurities.
- To lift safety valves rope should be used on the body and bonnet in accordance with fig. 2. Do not lift the valve at the lifting lever
- The valve should be mounted in a vertical position. After installing the valve, loosen the lever by removing the wire.
- Pipes connected to the valve should comply with the requirements included in the surveillance provisions. Crosssection and shape of the pipes should be selected so that they do not reduce the capacity of the valve. If the medium is discharged with one pipeline froma few safety valves, free area of the flow of this pipeline should be at least equal to the total area of outlet ports flow of these valves. Moreover, the pipes should be made advantageously to the flow (gentle curves). For valves equipped with drainhole condensate drainage should be used. For valves that do not have drainhole, drain should be provided at the lowest point of the discharge pipe.
- Full-lift safety valves from the range of 02 from DN 40 has a cast support lugs at the body, used with appropriate mounting to take the reaction forces over by the outlet.
- In order to avoid reaction forces at the outlet connection of the valve, it is required to use an appropriate support to the pipeline. The valve cannot act like a support structure for the pressure equipment on which it is mounted, and it cannot be exposed to deformation caused by installation of inlet and outlet pipes. When mounting the valve flange with the flange of the pressure equipment, use the appropriate gasket (adapted to the type of valve face and with respect to parameters and medium type). Flange bolts should be tightened evenly and with crisscross pattern. They should also be tightened after a certain period of operation of the valve or in the event of a leak. Mounting place of the valve should be easily accessible, good lighted and protected from external influences. If the safety valve is mounted outdoors, it must be protected against frost and rain. When mounted near the platforms for service, they must be in compliance with the provisions of Health and Safety Regulations (blowing valve should not be a threat to the health and life of people).
4. Operation of safety valves
Safety valves that serve as important elements of the devices and pressure systems require particularly careful and competent service. Any operational gasp may cause damage to the valve mechanism, and consequently lead to the total failure of the pressure system. Therefore, during the operation, pay special attention to:
- proper setting of safety valve, suitable for the operating parameters of the equipment being protected,
- proper protection of the valve mechanism against possibility of damage,
- periodically verification of correct operation of the valve, in accordance with the requirements of surveillance,
- proper maintenance and repair management. Checking the safety valve operation involves lifting of the disc with a lever, running it in the direction indicated in Figure 3. Starting the lever causes minimum lift of the disc and the flow of medium. Keep in mind that too frequent checking may result in damage to the sealing surfaces of the valve disc and seat and thus to a loss of tightness, and the complete lack of checking usually leads to “seizing" of the valve mechanism, what can have serious consequences.
The frequency of these activities depends primarily on:
- Working condition, i.e. the type of medium flowing and its parameters,
- The specifics of the technological process,
- Place of installation,
- environment. It should also be correlated with the test and repair of pressure equipment / installations that protects the valve. Very important is the experience of the user. Determining the periods of checking the safety valve is the responsibility of the designer of installation.
After checking of the valve, move the lever to the original position. When checking the valve there is a possibility of contamination the sealing surfaces. In this case, again lift disc to remove these pollutions. If tightness was not obtained by this, the valve needs to be regrinded from the next stop of the pressure device.
5. Adjustment of the set pressure Weight loaded valves do not have any elements allowing their regulation. It is recommended to send the valve to the producer for adjustment.
6. Maintenance and repair of safety valves
In order to ensure correct operation of safety valves, the following conditions must be met:
- valve disc cannot set slantwise to the valve seat;
- sealing surfaces of the seat and disc should ensure tight closure of the valve;
- all cooperating moving parts of valve mechanism should maintain movability in operating conditions. In order to maintain these conditions the valves should be periodically inspected and renovated. Inspections of safety valves should be conducted by persons with adequate authorisation. However, repairs should be first carried by manufacturer of the safety valve or by authorised by it service providers, or by user repair teams with appropriate surveillance permissions.
Zetkama Safety Valve Fig 570