4 replies to this topic

[E-Tantoy]

Good day to all!

I would juist like to ask if anyone has an idea what is the adjusting screw of a relief valve used for?
I am not sure about the actual operation (when the PSV pops), but isn't it that during the sizing of a
relief valve, we specify a specific set pressure and the highest contingency flow and calculate the required
orifice area. Then, why is there a need for the adjusting screw? Would there be any chance that we'll have
to adjust the set pressure (PSV is already installed)? If yes, can you give instances wherein we need
to adjust the screw.

Can we set it back again to its original set pressure?

Looking forward on your response.
Thank you very much!

[fallah]

Good day to all!

I would juist like to ask if anyone has an idea what is the adjusting screw of a relief valve used for?
I am not sure about the actual operation (when the PSV pops), but isn't it that during the sizing of a
relief valve, we specify a specific set pressure and the highest contingency flow and calculate the required
orifice area. Then, why is there a need for the adjusting screw? Would there be any chance that we'll have
to adjust the set pressure (PSV is already installed)? If yes, can you give instances wherein we need
to adjust the screw.

Can we set it back again to its original set pressure?

Looking forward on your response.
Thank you very much!

I think adjusting screw of a relief valve,let say conventional type,is to be used to compensate for constant superimposed back pressure.This may be provided by reducing the spring force.

Under these condition the spring force plus back pressure acting on the disc would be equal to the force of the inlet set pressure acting to open the disc.

As far as i know (may be not so correct),the range of adjusting by reduction the spring force could be up to 10% of set pressure for conventional PSV.

Edited by fallah, 26 October 2009 - 01:37 PM.

[Traileum]

Good day to all!

I would juist like to ask if anyone has an idea what is the adjusting screw of a relief valve used for?
I am not sure about the actual operation (when the PSV pops), but isn't it that during the sizing of a
relief valve, we specify a specific set pressure and the highest contingency flow and calculate the required
orifice area. Then, why is there a need for the adjusting screw? Would there be any chance that we'll have
to adjust the set pressure (PSV is already installed)? If yes, can you give instances wherein we need
to adjust the screw.

Can we set it back again to its original set pressure?

Looking forward on your response.
Thank you very much!

A time could arise where set pressure would need to be adjusted. For example, in a pipeline, if transfer pumps are changed out and a higher head is required to deliver more products, then there might be need for set pressure to be adjusted. Also during inspection, the set pressure could be off a little bit due to physical conditions of location different from where valve was shipped, distortions during shipment etc. In these cases you might have to reset the pressure so that it is right on the money. This is my understanding.

[JoeWong]

Adjusting screw allow you to reset the PSV when there is PSV set pressure change or backpressure change during plant debottlenecking or plant improvement. Normally once it is set in workshop and installed at site, it shall stay without any further adjustment at side. Any adjustment at site potentially cause incorrect PSV opening pressure.

Edited by JoeWong, 27 October 2009 - 12:17 PM.

[Michael Conway]

To All,
The PSV adjusting screw is used to adjust the set pressure on a valve. If there is a process change and the design pressure changes or the backpressure cahnges, the valve would need to be adjust to the new required set pressure. In most cases if there is backpressure I would recommend a balanced valve for the application. Also during maintenance of the valve the set pressure can drift some and the technician can adjust the valve back to the proper set pressure.