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Tickle, I have to disagree that thermal expansion, or fire are the only two ways to exceed the MAWP. Blocked discharge can cause overpressurization if the shut off head on the pump is higher than the MAWP, and there are non-locked-open block valves down stream of the filter. Jon

Hi, Yes it is possible for the PSV required flow rate to exceed the normal operating mass flow rate thru the filter. Since this is a simple filter, the only case that could likely exceed the blocked discharge (i.e. normal flow if you don’t take any credit for backing up on the pump curve) is...

Good morning, We need to be clear that sizing a valve, and determining the relief load are two different things. The first is simple (generally for 1 phase), and the other requires engineering skill and evaluation. The difficult one is determining the required relief load. This is how much...

Cutie, "my understanding correct: fire creates the greatest relieving requirements (biggest orifice size), the second is blacked discharge, then there is thermal (smallest orifice). If I go to a valve vendor without telling them it's thermal or fire, they would just size it as blacked...

Cutie, I sense it may be worth breaking down the whole basic process of sizing PSVs. Step 1: You need to consider all credible cases of over pressurization. These cases can include fire, blocked discharge, thermal expansion etc... Step 2: For each credible case you have to calculate how many...

Pleckner, I am glad to hear this question has made other people wonder as well. The only source of external heat that i have ever seen a relief load calculated for is for pool fires. Jet fires are not generally protected against with PSV (per API 521). Jonathan

Cutie, Since this is a filter, the main reason why you would need a thermal relief valve is if the minimum operating temperature is below the ambient temperature. In this case if the filter is blocked in, then heat from the atmosphere can increase the temperature of the fluid inside the filter...

ASME VIII states that a 21% overpressure should be used for fire or other unexpected sources of heat. I usually see "fire" interpreted as meaning a pool-fire. Does anyone have any examples of "unexpected external sources of heat?" Any example specific to refineries that you have designed for in...

A bit of a brain twister: What happens to either a centrigfugal or PD pump that has its discharge valve closed, and then subsequently the inlet valve closed. I know it will overheat, and explode/melt eventually. For the PD pump assume a PSV opens and disharges back to the suction line. For the...

Hello, I recently had a discussion about how much pressure difference or flow rate is sufficient for purging H2S from a blower casing. Due to a low casing design pressure, there were concerns that there was not enough driving force to get a sufficient purge. Does anyone know a reference to a...

Thank you everybody for your comments. I have given some further thought to my original question, and feel comfertable at this point. I will share my conclusions: 1) The psv SHOULD be sized for the "woosh" of nitrogen based on the worst case tank pressure (generally ~ 30 psig - assume truck PSV...

Hello, We have a storage tank that will be filled via truck deliveries. The truck will be pressurized to 20 psig with N2 to offload the inventory into the tank. I would prefer to use a pump, but the client prefers N2 offloading. A pressure regulator is designed to provide a maximum N2 flow of...

Thank you all. This is what i thought: That in steady state the flows should be the same. I have seen a configuration where both pumps have discharge control valves. It was explained to me that the control valve after the second pump was there to prevent the second pump from flowing more than...

COnsider two pumps in series. Pump A is feeding Pump B. A couple questions I have been stumbling over: Somebody has told me that it is possible for Pump B to flow at a higer rate than pump A and therefore draw a vacum on the suction side of Pump P. Is this actually possible? Or will as many...

Does anybody have any experience in designing instrumentation flush systems for instruments in slurry (FCC frac bottoms) service? Is it common to use intermittent or continuous flushes? Hardpiped? Any advice? Thanks. Jon

Just a little more info. The valve is a Dresser 3900 modulating pilot series, with a 2900 series heat exchanger installed on the pilot line. Thanks in advance to any help provided. Regards, Jonathan

I think this might contribute to chattering. If the inlet frictional losses exceed the blowdown setting. In the above case, once the PSV opens, the frictional losses will cause the PSV to close because the pressure at the PSV inlet will have dropped below the closing pressure (determined by...

Gerhardl, What we are most concerned about is potential freezing. Our ambient temperature can drop to about -20F. Did you have any problems with freezing? Many thanks. Jonathan

Thank you Gerhardl. Was the psv used in outdoor service? Regards, Jonathan

Hello, We have a pilot psv on a superheated 600 psig steam line. We operate close to the set pressure of the psv, hence a pilot psv was selected. We were told by the vendor that the maximum temperature the o-rings, etc... can handle is around 400 F. Therefore, there is a condenser on the...