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Shutoff head and Max Head @ rated Impeller

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gl99

gl99

Chemical
Oct 17, 2006
9
Hello All,
There is one 20 years pump without performance curve. We need the pump's shutoff head to evaluate the piping PSV set point. In data sheet performance section show max head @ rated impeller showed as 680 ft. Is this equal to shutoff head?

Thanks,
 
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I assume you can't reach the manufacturer.

The 680 feet as a shutoff point would be a good starting assumption. Is there anyway you could put the pump online and test it by pinching the pump and making your own curve? Even operating data taken over a several month time period could help.

Another way to get an estimate of the performance is researching other manufacturers curves of pumps with similar impellar sizes and adjusting for speed with the fan laws.

I know there are some generalized equations in the Hydraulic Institute Standards. But a 20 year old pump will have slip from wear.
 
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BEP-Hd is not the shutoff head. If you must assume something, typically the shutoff is 25-30% above your BEP head, but NOT ALWAYS.

Get a couple of points on the curve and extrapolate backwards to zero flow and you should be able to get a reasonable estimate of SOH, by subtracting your suction head from the value at that point.

Your shutoff head (and all pump heads) are differential heads, so you must add the suction pressure to the shutoff head (pressure) to find the maximum discharge pressure to use when you evaluate your PSV setting.



BigInch[worm]-born in the trenches.
 
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If you're talking a centrifugal, max head at rated is, obviously, the maximum head that the impeller as sold will develop. Is it still the same impeller? Also, depending on the pump, max head may not be at shutoff. What make, model, etc are you talking about?
 
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Maximum head @ rated impeller could indicate shut head or it could also mean maximum head at the duty flow.

What other information is on the data sheet - does it give a duty point (eg, 500gpm @ 640ft)? - this is the performance with selected diameter impeller at the operating speed. If the data sheet contains this type of information you are probably safe in assuming that the 680ft is the shutoff head.

Alternately, take a pressure reading of the pump discharge during normal operation, use this pressure as a base and then add a margin to this pressure and set your own PSV setpoint.

Phitsanulok
Thailand
 
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Hello All,

Thanks for you guys answer for my question. This is a vertical centrifugal can pump. The vendor has out of the market. So I tried to size one new pump per existing pump datasheet information. From flowserve Pro+ pump selection software, I got one pump performance data, the shutoff head based on pump curve is equal to pump maximum head @ rated impeller from datasheet. (Assume you have the rated size impeller.)
So I think my assumption that shut off head equal to or higher than shutoff head is correct.


Thanks,

gl99
 
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Your assumption is usually correct, but so what?

Don't set your PSV higher than the pipe allowable (and all other downstream equipment). The PSV is there to make sure your system doesn't see pressures higher than it is rated for. The sys's maximum allowed operating pressure is what you need to find out. If your sys's maximum allowed operating pressure is higher than your pump's shutoff head pressure equivalent, you just might not even need a PSV.

BigInch[worm]-born in the trenches.
 
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If the pipe and equipment downstream of the pump is rated at a pressure greater than the pump can supply I would question installation of a PSV. You still have to investigate other sources that could increase the pressure on the downstream pipe and equipment, such as fire, solar thermal, heat exchangers, reactors, ect. If these outside forces can increase the pressure a PSV will be require, but it will be a lot smaller.
 
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I've been watching this post and finally saw mentioned the one series of statements that are dangerous:

BigInch: "If your sys's maximum allowed operating pressure is higher than your pump's shutoff head pressure equivalent, you just might not even need a PSV."

dcasto: "If the pipe and equipment downstream of the pump is rated at a pressure greater than the pump can supply I would question installation of a PSV."

BigInch, shame on you, we've had this discussion before.

Except for some very specific exclusions, if the equipment downstream of this pump is/are ASME Coded, it/they will require a PSV, even if it is only a simple 3/4" x 1" designated for thermal relief...period.
 
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pleckner, whooo.

If the equipment (if there is any equipment, the OP doesn't mention it; the only clue is he's a chem) needs a PSV because its code equipment and that code requires it, the PSV needs to be on the equipment; NOT ON THE PIPE.. period & exclamation! If the equipment has a block valve, like they usually do, a PSV on a pipe won't ever help it. There are pleanty of pipe-only systems that do not have any PSV's anywhere. The pipe and pump doesn't need a PSV, if the pipe can withstand the shutoff pressure, surge pressure, and the closed in product's thermal expansion pressure. And I said "might" and nobody said anything about ASME, or vessels downstream, except you.

That said, you know this is an engineering tips forum and there is no way you, I or we can perform a total design review to see if a PSV is needed somewhere in the system or not, especially when any such equipment is a figment of our imagination that was entirely unmentioned by the OP. Neither should we be judgemental about the OP's IQ. You must give them some credit, although I agree sometimes its difficult. Half the stuff they ask here they should be asking their supervisors, rather than trying to find some magic bullet to make them look good. What are we supposed to do? I'm just shooting to keep my answers reasonably specific to the question and reasonably qualified, given the little information we usually get, without getting off too far on imaginary tangents. You can't believe its our job to teach them how to do theirs. Frankly I don't have the time to give an entire list of cavets and qualifications for a free tip.

BigInch[worm]-born in the trenches.
 
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pleckner, shame on you for not reading all your papers.

"You still have to investigate other sources that could increase the pressure on the downstream pipe and equipment, such as fire, solar thermal, heat exchangers, reactors, ect. If these outside forces can increase the pressure a PSV will be require, but it will be a lot smaller."

And by the way, the Federal DOT inspectors agree with my statement about no relief valves or for that matter, any over pressure protection device on our 2280 psi pipeline (B31.8 with B31.3 metereing) that went through a Houston because we demonstrated that the pipeline pumps could not supply enough head pressure to over pressure the pipeline.

As for a Chem E, I've done more ME work than most ME's.





 
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Yeah, I was describing a system without a PSV. As always you have to see all the parts. The lines are buried so there are no solar or fire cases that would create a need for protection. The fluid was compressible enough it didn't have a surge large enough to make that an issue.

In lieu of PSV's on line that are subject to overpressure from a thermal source, a 1/2" check valve around a block valve can be used.
 
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Dear All,

I am very appreciate your guy’s help for my question. As all of us know, we have to review all potential release cases (fire, tube rupture, thermal, block out etc.) for PSV design. One post question can not result big project and I do not want release all the project information in the public forum. Here is pump forum and that is why I just force on this particular pump performance question and seek the answer from vendor and work colleagues and your guys at same time. Eng-tip is one forum which is free and open to all of us. I assume all of us are Professional Engineer and deeply know the basic ethic of a professional engineer. "Do not do to others that which would anger you if others did it to you”.
Please respect to each other and keep this forum open to all the people and give your valuable answer for all of us.
Thanks,
Best regards,
 
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OUCH, Gang-up time!

I was trying to be a little tongue-and-cheek here.

BigInch, the reason I even bothered to put my 2-cents worth in to this discussion was because the word equipment was mentioned in the same breath as PSV..by you, "Don't set your PSV higher than the pipe allowable (and all other downstream equipment)." I was perfectly content to leave this discussion about pumps and pipe lines in your expert hands.

Once the concept of equipment and PSV was brought into this conversation, I have to assume ASME or equivalent compliance, otherwise, as dcasto points out, why bother bringing it up. And you and I have discussed this before about PSVs on pipes, no need to rehash it, not to mention that we are in complete agreement on the subject.

Also, couldn't agree with you more about trying to teach or about the time we have to dedicate to giving advice but we must be careful we don't leave very important strings dangling either. They may be taken and interpreted the wrong way, and often are.

"dcasto", Sorry but your fist sentence is what made me concerned, not the second post,which I did read.

And guys, yes, I'm guilty of assuming ASME jurisdiction here, especially since we are dealing with only about 700 feet of pressure head, not 2000 psig.

Guys, let's be friends.
 
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No problemo, I'm guilty of not reading an entire responce so I answer too quickly. Sorry if I accused you of anything.


 
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