8 replies to this topic

[Sridhar P]

Dear Sir,

In one of the pump specifications, it is mentioned a minimum shut-off head of 15% more than the design head.

Why it is required. what if shut off head falls within 15% margin on design head.

Kindly clarify.

Thanks and Regards,
P.Sridhar

[fallah]

Dear Sir,

In one of the pump specifications, it is mentioned a minimum shut-off head of 15% more than the design head.

Why it is required. what if shut off head falls within 15% margin on design head.

Kindly clarify.

Thanks and Regards,
P.Sridhar

Sridhar,

In basic design stage while the pump performance curve isn't available, it (shut-off head) is required to estimate the design pressure of piping and equipment located in pump downstream. For most pumps with almost flat curve 1.15 times of the design head could be a proper estimation.

Fallah

[S.AHMAD]

I normally use 1.20 to be more conservative. The shut off head is depending on the pump design (specific speed). For low specific speed e.g. 500 ~ 700, the performance curve is almost flat so 1.15 is adequate.

The shut-off pressure is normally used to decide on the casing and piping design after taking into consideration the maximum possible suction pressure ( e.g. relief valve pressure + elevation head).

[Sridhar P]

Dear Sir,

Kindly let me know in the implication on pump performance, when shutoff head is less than 15% of design head.

The specification reads like this,

"The total head capacity curve shall be continuously rising from the operating
point towards shut-off without any zone of instability and with a minimum
shut-off head of 15% more than the design head."

Thanks and Regards,
P.Sridhar

[Virginia]

If you have calculated the pump downstream design pressure using more than 15 % value then you are fine even if vendor gives shut off of 15 % of design head.
Had he given more than 15 % it would have been a problem.
I would advise your ask for the performance curves from vendor to calculate the actual shut off with the highest density case to ensure the design pressure doesn't exceed your earlier estimate.

[djack77494]

You normally want to be able to control the flow of liquids through the pump. Typically, you do so by throttling a control valve in the discharge line of the pump. As you do so, you push the pump's operating point backwards along its curve. If the curve is overly flat, say less than 15% rise from design to shutoff, then it is not very controllable by this method. Small changes in your final control element (the valve) will have a large impact on the flow through the pump, which is an undesirable situation. Avoid this by specifying that the curve rise at least 15% from design to shutoff. (Though this is an arbitrary value, it provides for reasonable flow control.)

[Bodhisatya]

Please help me....by telling What Shutoff Pressure Actually is??????Sorry 4 asking this stupid question but I want to clear my fundamentals

[Virginia]

Please refer to a pump performance curve. As the flow is reduced, the differential head increases. When the discharge valve of the pump is closed the flow reduced and the differential head increases. Shut off head is defined as differential head at 0 flow through pump. This is being most conservative , it is used to calculate discharge design pressure of the pump.
When the performance curve is not available, 120 % of rated head is considered as the shut off head.

[breizh]

http://www.pumpfunda...m/pump_book.htm

Consider this resource ( free download) . It will support your query .

Breizh