Psv Sizing

Hi,

I am trying to find the minimum orifice size for a PSV for boiler feed water at set pressure 2000kpag, relieving pressure at 2200kpag at 2626kg/hr (43.75L/min)

Based on API 520, for Liquid Relief Requiring Capacity Certification, my minimum orifice size is 17.298mm².

So this would mean I would select orifice designation D based on API 526 at 71mm². 

I am wondering what the repercussions are, if any, for selecting an orifice size that seems to be much bigger relatively.

Additionally, would like an idea of what happens in the hypothetical situation that the vendor supplies a PSV one size up (E). 

Thanks 

 

I am trying to find the minimum orifice size for a PSV for boiler feed water at set pressure 2000kpag, relieving pressure at 2200kpag at 2626kg/hr (43.75L/min)

 

Based on API 520, for Liquid Relief Requiring Capacity Certification, my minimum orifice size is 17.298mm².

 

So this would mean I would select orifice designation D based on API 526 at 71mm². 

 

I am wondering what the repercussions are, if any, for selecting an orifice size that seems to be much bigger relatively.

 

Additionally, would like an idea of what happens in the hypothetical situation that the vendor supplies a PSV one size up (E). 

 

speakas,

There are thousands of other non API 526 valves which are ASME certified but they’re a different type of valve from API 526 valves. Many of these are tiny valves that you can apply for your requirement. A “D” orifice is the smallest API 526 orifice, but there are many ASME certified valves that are smaller than a “D”.

Hence, to avoid the probable consequences such as chattering, try to find a small non API valve having an orifice area not more than a few percent, say 25%, higher than the required relief area.

 

 

I am trying to find the minimum orifice size for a PSV for boiler feed water at set pressure 2000kpag, relieving pressure at 2200kpag at 2626kg/hr (43.75L/min)

 

Based on API 520, for Liquid Relief Requiring Capacity Certification, my minimum orifice size is 17.298mm².

 

So this would mean I would select orifice designation D based on API 526 at 71mm². 

 

I am wondering what the repercussions are, if any, for selecting an orifice size that seems to be much bigger relatively.

 

Additionally, would like an idea of what happens in the hypothetical situation that the vendor supplies a PSV one size up (E). 

 

 

speakas,

 

There are thousands of other non API 526 valves which are ASME certified but they’re a different type of valve from API 526 valves. Many of these are tiny valves that you can apply for your requirement. A “D” orifice is the smallest API 526 orifice, but there are many ASME certified valves that are smaller than a “D”.

Hence, to avoid the probable consequences such as chattering, try to find a small non API valve having an orifice area not more than a few percent, say 25%, higher than the required relief area.

 

Thanks for the prompt reply fallah,

Just to clarify, I am led to believe that ASME certification do not come in "standard" sizes such as the API 526 sizing. So am I correct to assume that any orifice supplied by a fabricator/vendor that is ASME certified will be good enough for use as long as it does not exceed the 25% of the minimum area as calculated through API520?

Regards,