4 replies to this topic

[lilwa]

Why we have multiple relief devices/valves for pressure relief rather than a large, single relief device/valve? (For example the relief capacity of 250 tons/hr for a boiler. Two phase material)

The set pressure for multiple relief valves is oftenly different. Why we need to keep same of different pressure set points.

[Bobby Strain]

For boilers, two valves might be required by location jurisdiction of some government agency.

[fallah]

Why we have multiple relief devices/valves for pressure relief rather than a large, single relief device/valve? (For example the relief capacity of 250 tons/hr for a boiler. Two phase material)

The set pressure for multiple relief valves is oftenly different. Why we need to keep same of different pressure set points.

 

lilwa,

 

Multiple PSV's configuration is applied when there is very high relief load such that a single PSV, even a maximum size among selected vendor products, cannot handle that load and it should be handled by several PSV's...

Also this configuration is applied when there is so difference between lowest and highest relief loads of all scenarios, say the ratio of min/max is almost lower than 0.25, and there is the possibility of single PSV chattering in lower loads...

 

The set pressures of multiple PSV's should be different mostly to avoid possible chattering might be happened due to all PSV's getting started to open simultaneously...
 

Edited by fallah, 30 May 2016 - 01:46 PM.

[S J]

lilwa

As Bobby and fallah mentioned above,

If you mention boiler, steam boiler shall follow ASME sec I.

In accordance with ASME sec I, PG-67,

" Each boiler shall have at least one pressure relief valve and if it has more than 500 ft2 (47m2) of bare

tube water-heating surface, or if an electric boiler has a power input more than 1,100 kW,

it shall have two or more pressure relief valves. For a boiler with combined bare tube and extented

water-heating surface exceeding 500 ft2 (47m2), two or more pressure relief valves are required

only if the design steam generating capacity of the boiler exceeds 4,000 lb/hr (1800 kg/hr). ..."

And when I performed some projects, staggered set pressure applited to multiple PSVs to minimize chattering.

[lilwa]

Thanks all! So nice of you.