Is high pressure differential always a bad thing?

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Discussion Overview

The discussion centers around the implications of high pressure differentials in various mechanical systems, particularly in relation to equipment such as valves, pumps, filters, and turbochargers. Participants explore whether high pressure differentials are inherently negative or if they can be beneficial in certain contexts, including control systems and flow measurement.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that high pressure differentials are generally detrimental as they can lead to energy loss through heat and vibrations, affecting equipment lifespan.
  • Another participant counters that a high pressure differential across filters or strainers indicates clogging and is undesirable, while noting that significant delta P is necessary for accurate flow measurements in orifice plates.
  • A participant mentions that high pressure differentials are essential for the operation of turbochargers.
  • It is noted that high pressure differentials across control valves are necessary for precise control, although there is a request for clarification on this point.
  • One participant elaborates that if a control valve is too large, a high pressure drop may not occur until nearly fully closed, which could lead to poor flow control accuracy.
  • Another participant discusses the role of pressure differentials in solenoid valves, initially expressing uncertainty but later acknowledging the importance of pressure balance in valve operation.
  • Concerns are raised about the potential for high velocities through oversized valves leading to cavitation and control issues.

Areas of Agreement / Disagreement

Participants express differing views on the implications of high pressure differentials, with some arguing they are generally negative while others highlight specific scenarios where they are necessary or beneficial. The discussion remains unresolved regarding the overall impact of high pressure differentials across different applications.

Contextual Notes

Participants reference specific applications and conditions under which high pressure differentials may be advantageous or problematic, indicating a need for careful consideration of system design and operational parameters. There are also mentions of specific limitations in valve sizing and flow control accuracy that remain unresolved.

Ask1122
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Hi all, was thinking about this the other day. Is high pressure differential always a bad thing?
Please correct me if i am wrong, but from the way I understand, high pressure differential is bad because if you have a high pressure differential across a piece of equipment (valve, pump, fitting etc...), it means that some of the pressure energy are probably converted into heat and vibrations, which will effect your equipment lifespan.
But for something like strainers/filters, wouldn't a high pressure differential be actually a desired characterisitc?
 
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A high delta P across a filter or a strainer is how you tell if they are clogged and not operating properly. So no, you do not want a high delta P across them. Think of it this way, if you take a big drop across something, that is wasted energy. There are times you want a significant delta P, for example, an orifice plate. You need to have a somewhat sizeable drop across the plate to have meaningful pressure measurements for your flow calculations.
 
A high pressure differential across a turbocharger is what makes it work...
 
Good point Brews.
 
A high pressure differential across a control valve is necessary for precise control.
 
russ_watters said:
A high pressure differential across a control valve is necessary for precise control.

Can you please elaborate on that? I thought that it's the other way around, that the high delta P is the side effect of the control valve when the valves are in a throttling position?
 
When you close a control valve, the pressure drop goes up, yes (obviously). But what if it didn't go up much? If you close a valve 99% of the way and the pressure drop doesn't go up noticeably because the valve is way too big, you won't have changed the flow much either. Then in the last 1% of valve travel, you'll completely shut off the flow. If your valve position accuracy is 1%, your flow control accuracy is plus or minus abouot 100%.
 
pressure differential also is what keeps may solenoid valves closed. If you turn them around, they leak, because the pressure lifts the seat.
pressure differential is also what makes pumps pump.

dr
 
dr dodge said:
pressure differential also is what keeps may solenoid valves closed. If you turn them around, they leak, because the pressure lifts the seat.
pressure differential is also what makes pumps pump.

dr
I'm not so sure of that. Can you provide an example? In my work, the piloted solenoid valves I have seen use the upstream system pressure to keep the valve closed or to provide opening motive force. I can't say I have ever heard of one that relies on the delta P for this. Most solenoids are limited on the delta P they can take across them. Maybe I am just looking at them in different way.

EDIT: I guess, after thinking about it a little more, there is the need for the low side to set up your force balance in the valve. So you are correct. Never mind.
 
  • #10
russ_watters said:
When you close a control valve, the pressure drop goes up, yes (obviously). But what if it didn't go up much? If you close a valve 99% of the way and the pressure drop doesn't go up noticeably because the valve is way too big, you won't have changed the flow much either. Then in the last 1% of valve travel, you'll completely shut off the flow. If your valve position accuracy is 1%, your flow control accuracy is plus or minus abouot 100%.
You will be forced to run a valve that is too big in that last few percent open range which will also probably lead to very high velocities through the valve, which lead to high losses and possible cavitation and flashing in the valve. The controlability will be shot because very small valve movements will have large effects. Not a good place to be indeed.
 

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