5 replies to this topic

[deltaChe]

We all know that different control valve style will have different relative shutoff capability

such as Reg-Sliding stem, bar stock, partial ball all have excellent shut off capability.

And, choosing appropriate max shutoff pressure of control valve to assure leak tight shut off is important.

The question following is very simple and trivial. Please bear with me.

Our instrument staffs ask us(process) to recheck that 1.5 times the control valve max shutoff pressure (base on licenser Flour’s rule) has to be greater than these system design pressure/pump shut off pressure/supply pressure to avoid the control valve’s actuator to break off. But in my experience, most of the control valve’s max shutoff pressure is only barely greater than their design pressure.

N1. Why does 1.5 times rule is necessary?

N2. If the CV max shutoff pressure smaller than pump shutoff pressure, it may cause that valve hardly to close or open? Can anyone kindly explain the detail reason behind this?

N3. Do we have to put the bypass valve to balance the both side pressure if the CV max shutoff pressure smaller than pump shutoff pressure



Thank you very much for your kindly help.

[daryon]

We all know that different control valve style will have different relative shutoff capability

such as Reg-Sliding stem, bar stock, partial ball all have excellent shut off capability.

And, choosing appropriate max shutoff pressure of control valve to assure leak tight shut off is important.

The question following is very simple and trivial. Please bear with me.

Our instrument staffs ask us(process) to recheck that 1.5 times the control valve max shutoff pressure (base on licenser Flour’s rule) has to be greater than these system design pressure/pump shut off pressure/supply pressure to avoid the control valve’s actuator to break off. But in my experience, most of the control valve’s max shutoff pressure is only barely greater than their design pressure.

N1. Why does 1.5 times rule is necessary?

N2. If the CV max shutoff pressure smaller than pump shutoff pressure, it may cause that valve hardly to close or open? Can anyone kindly explain the detail reason behind this?

N3. Do we have to put the bypass valve to balance the both side pressure if the CV max shutoff pressure smaller than pump shutoff pressure



Thank you very much for your kindly help.

1. I think it's typical to specify the upstream design pressure for shut-off, perhaps the 1.5 times rule is to ensure that the actuator is guaranteed to be sufficiently sized to open the valve under shut-off conditions. May be in Flour's past experience sizing the actuator for the shut-off pressure has resulted in valves that won't open when the condition is realised and hence they now specify a hefty margin. Better to be safe than sorry.

2. If the shut-off pressure has been under specified i.e. less that the pump shut-off pressure then in the scenario that one side of the valve is exposed to the pump shut-off pressure whilst there is low pressure the other side the actuator my not be able to generate sufficient torque to open the valve.

You may find the following article relevant and interesting it's about ESDV shut-off DP - and torque calculations and associated actuator sizing - but still relevant to your query:
http://www.safetyuse...EN/AR060001.pdf

3. You may have to, if the actuator is undersized then a small bypass line to pressurise the downstream system and reduce the differential pressure across the valve may be required. In this scenario there maybe no other way to get the control valve to open. But why are you planning to observe pump shut-off pressure? It's not advisable to dead head pumps, you should have a pressure trip on the discharge to stop the pump reaching shut-off pressure.

[AZIZ_MN]

hi hswang2,
we have got same problem,our one of feed pump discharge > 32barg and from this 1" line is going to pump seal flushing with pressure control PIC with set pressure <7 barg,delta P across the valve is very high as d/s of controlvalve is only 20 mbarg due to that it is stuckingup in close position,and bypass of contorol valve can not be open due to safety valve will get pop if it is overpressure, i'm curious to know how to design 1" control valve with such high delta pressure

Edited by azzu, 22 July 2010 - 11:16 PM.

[fallah]

hi hswang2,
we have got same problem,our one of feed pump discharge > 32barg and from this 1" line is going to pump seal flushing with pressure control PIC with set pressure <7 barg,delta P across the valve is very high as d/s of controlvalve is only 20 mbarg due to that it is stuckingup in close position,and bypass of contorol valve can not be open due to safety valve will get pop if it is overpressure, i'm curious to know how to design 1" control valve with such high delta pressure

That seems to be an interesting issue!

Let us have a simple sketch for better understanding and also assistance.

Edited by fallah, 23 July 2010 - 01:40 AM.

[AZIZ_MN]

hi hswang2,
we have got same problem,our one of feed pump discharge > 32barg and from this 1" line is going to pump seal flushing with pressure control PIC with set pressure <7 barg,delta P across the valve is very high as d/s of controlvalve is only 20 mbarg due to that it is stuckingup in close position,and bypass of contorol valve can not be open due to safety valve will get pop if it is overpressure, i'm curious to know how to design 1" control valve with such high delta pressure

That seems to be an interesting issue!

Let us have a simple sketch for better understanding and also assistance.

Hi fallah
herewith i attached sketch

Attached Files

•  Book1.xlsx   30.32KB   175 downloads

[sukubutsu]

hi hswang2,
we have got same problem,our one of feed pump discharge > 32barg and from this 1" line is going to pump seal flushing with pressure control PIC with set pressure <7 barg,delta P across the valve is very high as d/s of controlvalve is only 20 mbarg due to that it is stuckingup in close position,and bypass of contorol valve can not be open due to safety valve will get pop if it is overpressure, i'm curious to know how to design 1" control valve with such high delta pressure

That seems to be an interesting issue!

Let us have a simple sketch for better understanding and also assistance.

Hi fallah
herewith i attached sketch

Hi All,

Was just wondering if the question posed by Azzu was resolved in another discussion forum. If not, can someone please give their input. I too would like to know what others recommendations are.

Thanks