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Significance of Pump Shut Off Head
- Thread starter RJSH
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For the analysis of Process Safety, you need to understand the maximum pressure that a pump could deliver. Any portion of the downstream system that could be exposed to this pressure needs to be designed to accommodate that pressure or be protected against it by appropriate Pressure Relief Valves. If there is a realistic scenario where the pump could be blocked at the outlet to zero flow, the portion of the system that could be exposed to that pressure must be able to safety withstand that pressure. This is the most common reason I would be concerned about the dead-head pressure of a centrifugal pump.
Johnny Pellin
Johnny Pellin
petrochemical87
Chemical
As JJPellin points out the shutoff head influences the design pressure of the discharge piping and the pump casing itself. From the operations/maintenence point of view, operating at the extreme left on the pump curve for extended periods of time can cause serious problems with the pump seal and the pump itself(due to temperature rise of the fluid and increased radial thrust). I have seen several pumps that are designed to trip on low flow to protect the pump.
QualityTime
Civil/Environmental
If you shut in the pump and allow it to run for an extended period of time the water in the casing will heat up. If left like that for a long time you could cause damage to the casing and seals.
From a pump operation point of view, in municipal water treatment plants and pumping stations we always start the pump up against a 95-100% completely closed valve and then slowly fully open it up. This allows the water to be pumped into a distribution system slowly at first. This protects the distribution system from sudden surges. On pump de-energization, the discharge valve is slowly closed to 95% closed and the pump is then de-energized. The valve continues to 100% closed. This again prevents surging and water hammer in the distribution system
The shut in head is the maximum pressure your motorized discharge valve operator has to be able to overcome and the motorized valve operator manufacturer needs to know this. The same goes for the valve itself
From a pump operation point of view, in municipal water treatment plants and pumping stations we always start the pump up against a 95-100% completely closed valve and then slowly fully open it up. This allows the water to be pumped into a distribution system slowly at first. This protects the distribution system from sudden surges. On pump de-energization, the discharge valve is slowly closed to 95% closed and the pump is then de-energized. The valve continues to 100% closed. This again prevents surging and water hammer in the distribution system
The shut in head is the maximum pressure your motorized discharge valve operator has to be able to overcome and the motorized valve operator manufacturer needs to know this. The same goes for the valve itself
There is one nice thing about shut-off head. If you do not have a good flow meter, you can still run the pump at dead-head for a few seconds and record the pressure. This gives you one point to evaluate the condition of the pump against the original test curve. But, as is noted above, running there for more than a few seconds is unwise. And, if the pump is a very high energy design (multi-stage or high speed single stage) it may not even be advisable to run at dead-head for a few seconds to measure pressures.
Your question is not clear. What are you wanting to do or needing to do?
Johnny Pellin
Your question is not clear. What are you wanting to do or needing to do?
Johnny Pellin
- Thread starter
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QualityTime
Civil/Environmental
"....A pump running at shutoff will add 42.4 Btu/min per HP at shutoff. If a pump casing holds 100 lbs of water and S.O. HP is 100BHP, then running at shutoff will add 42.4 Deg F per minute! That won't take long to smash and crash something..."
A lot of the heat will get dissapated to the surrounding piping which is full of "cooler water" so that buy you some float time
A lot of the heat will get dissapated to the surrounding piping which is full of "cooler water" so that buy you some float time
"A lot of the heat will get dissapated to the surrounding piping which is full of "cooler water" so that buy you some float time." That will depend on where the pump is actually isolated from the pipework, at the discharge via a valve then there is no buffer from pipework / cooler water.
Also, maximum shaft deflection is at CV, it is also inadvisable to run any high energy pump too far left on its performance curve at any time for obvious reasons.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
Also, maximum shaft deflection is at CV, it is also inadvisable to run any high energy pump too far left on its performance curve at any time for obvious reasons.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
PersonalProfile
Mechanical
OEMs typically provide a "min flow" below which operation is not recommended.
There is a clear distinction between centrifugal and axial pumps, most of the concepts expressed here refer to centrifugal pumps. Just one comment: shut-off head IS NOT the shut off pressure, the shut off pressure is the result of adding the head converted to pressure (divide head by specific weight of fluid) plus (or minus) static head also converted plus hydraulic pressure + any dynamic (transient) effects caused by the operation (water hammer, cavitation, flashing, etc).
what is important to know is that the oem provides data for their pump ONLY, the user must integrate the pump data into the system under consideration
saludos.
a.
There is a clear distinction between centrifugal and axial pumps, most of the concepts expressed here refer to centrifugal pumps. Just one comment: shut-off head IS NOT the shut off pressure, the shut off pressure is the result of adding the head converted to pressure (divide head by specific weight of fluid) plus (or minus) static head also converted plus hydraulic pressure + any dynamic (transient) effects caused by the operation (water hammer, cavitation, flashing, etc).
what is important to know is that the oem provides data for their pump ONLY, the user must integrate the pump data into the system under consideration
saludos.
a.
Pump shut off head, if lower than the head on any other part of the curve results in what is called a "drooping curve. Such a pump is not stable in parallel or even single operation.
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Another reason is to find out if your design head and impeller sizing are correct and demonstrated in the field. Shut-off testing is one of the first things to test using AABC and NEBB standards. That's why it's always good to have a dP or test ports across pumps.
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