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delivery pipe

delivery pipe

delivery pipe


I have a 2'' gear pump.

Is it ok to use a 3'' delivery pipe or will it effect the Q because of less pressure?

Best Regards
Roman Katz

RE: delivery pipe


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.)

RE: delivery pipe

Interestingly, this one of those questions that can actually be answered with very little information. Generally, Roman, positive-displacement pumps will deliver whatever discharge pressure is required to meet their fixed flow rate.

The only way in which potentially 3" delivery pipe would limit your flow is your extreme cases where you've been working with a system with much larger piping and changing your pipe size increases the system resistance to such a degree that you start overpressurizing your system and losing flow to the relief path. Slippage can also be a problem at higher discharge pressures, but will only be a fraction of the flow that you'll probably gain.

RE: delivery pipe

The OP needs to re-read the extensive info given previously on his earlier question.

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.)

RE: delivery pipe

Gotcha - didn't realize that he had gotten feedback previously.

OP - please provide links to associated posts if they pertain to a similar system (or copy in the relevant information).

Edit: Just read your previous post - http://www.eng-tips.com/viewthread.cfm?qid=423001.

RE: delivery pipe

Thank you all.

Best Regards
Roman Katz

RE: delivery pipe


I'm not sure you really grasped the nettle of what the other posts says as repeated by adam above.

Your gear pump at a fixed speed will try to flow virtually the same flow through it until it hits either the torque limit of the motor or excess power trip or the internal or external pressure relief limit.

How much flow you will get is dependent on these limits and the downstream system. A bigger pipe has, in general, less frictional resistance for the same flow rate. Your pump only sees the back pressure from the system. As the flow is essentially fixed, shaft power is proportional to pressure. Twice the pressure required to move the same flow, twice the shaft power required to do it.

does that make sense?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: delivery pipe

Yes, thank you.
This is a much lower viscosity oil (10 cst) so i believe it will work out.

Best Regards
Roman Katz

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