RE: pumps in series

Hi S. Paramesh

If there is no flow in the line, then the pressure will be in excess of the existing 3 bar pipeline pressure plus the 4 bar pump pressure. The reason why it is in excess it that the pump will generate more head at zero flow than it will at 20m^3/h.

If the line is currently flowing 20m^3/h and continues to do so after the pump is fitted, then the pressure at pump discharge will be 3+4= 7 bar. However a booster is normally fitted to give more flow. The extra flow and final pressure cannot be estimated from the information you have provided, but the pressure would not be more than 7 bar.

If the line is currently flowing far in excess of 20m^3/h, then fitting the pump could actually result in less pressure at discharge than what is there now. The reason is that pumps produce head but also have internal friction loss. The friction loss increases approximately as the square of the flow rate. On a fixed speed pump the head produced near shutoff is the maximum that the pump can produce. As the flow increases the head drops off, due ,in part, to friction. If the flow is high enough the friction loss can exceed the generated head. The motor will normally overload before this condition arises.

So you see that even in terms of basic principles, the information you have provided is insufficient to answer your question.

You may wish to have a look at some of the information available through www.fluidedesign.com and <a href="/group/PipingDesign/post?postID=dRjBNPKHU3M1dXpZ7hxtG-gRPPlwIiMVDSMwfoHevWz8gLiYgWjYzuy4HKnC-B5Lm9IixvKjhqc8R6ISfDofY2y-d5g_Z63Cj67q">centrifugal_pumps@yahoogroups.com</a> Also please direct any future correspondence to <a href="/group/PipingDesign/post?postID=qNuNO6wLDMcwja-o_a7f6JXOWzQYxrP80YBlXDTURa8ek-cTHlJB7eY5j6QN5Asa9Ell9aj1fBANxO16sVFWQV4Uz3Lo48E">PipingDesign@yahoogroups.com</a>

Cheers

Steve McKenzie

-----Original Message-----
From: saiparam [mailto:saiparam@yahoo.co.in] Sent: Friday, August 29, 2003 1:58 AM
To: Steve McKenzie
Subject: Re: pumps in series

Dear Mr. Steve

Thanks for your reply. OK. I did not give the basic info' as required by you. Because I do not have them. What I have only are informations given in my message. I am not expecting the accurate figures or values regarding the discharge pressure and flow rate. All I want to know is when a 3 kg/sq.cm(g) water piping is connected to a centrifugal pump (20cum./Hr & 40mlc total head)what will be the discharge pressure in PRINCIPLE? Whether the discharge (say immediatly at the pump discharge) will be more than 40 mLC or will not cross 40 MLC? Pl. enlighten me with your clarification. As this problem deal with the fundamental of centrifugal pumps, I want to be clear of principles. Again I request you to not to worry about the detailed information.

Thanks and Regards

S. Paramesh

• In PipingDesign@yahoogroups.com, "Steve McKenzie" <Mechproj@x> wrote:
  > Hi S. Parameshwaran
  >
  > your question cannot be answered with only the information your have
  > provided.
  >
  > Whether or not the flow will increase depends on what the flow is
  now, and
  > the pump curve.
  >
  > Whether or not the pressure will increase depends on what the system
  > resistance curve is like.
  >
  > You need to get enough information to describe a system resistance
  curve,
  > and a pump curve.
  >
  >
  > Cheers
  >
  > Steve McKenzie
  >
  >
  > -----Original Message-----
  > From: saiparam [mailto:saiparam@y...]
  > Sent: Thursday, August 28, 2003 1:25 AM
  > To: <a href="/group/PipingDesign/post?postID=qNuNO6wLDMcwja-o_a7f6JXOWzQYxrP80YBlXDTURa8ek-cTHlJB7eY5j6QN5Asa9Ell9aj1fBANxO16sVFWQV4Uz3Lo48E">PipingDesign@yahoogroups.com</a>
  > Subject: [PipingDesign] pumps in series
  >
  >
  > This may be a general question. Yet, I want an engineering answer.
  >
  > The question:
  >
  > A centifugal pump is required to be connected to a water pipeline (3
  > inch CS), which is already having a pressure of 3kg/sq.cm(g) in it.
  > The proposed pump is having a capacity of 20 cu.m/hr and 40mLC head.
  >
  > The pump was not selected for booster applications, but an ordinary
  > pump available as a spare. Now, what will be the discharge pressure
  > and effect on pumping rate if, the 3kg/sq.cm(g) piping is connected
  > to this pump?
  >
  > Immediate replies are highly appreciated.
  >
  > S. Parameshwaran
  >
  >
  >
  >
  >
  

  ---

  ---

  
  > ==============
  > Discussion List sponsor: The fluid flow calculations website -
  > www.LMNOeng.com - LMNO Engineering, Research, and Software, Ltd.
  >
  

  ---

  ---

  
  > ==============
  >
  > Your use of Yahoo! Groups is subject to
  <a href="http://docs.yahoo.com/info/terms/">http://docs.yahoo.com/info/terms/</a>