Reducer on discharge side of cent. pump
Reducer on discharge side of cent. pump
(OP)
Hi,
I know it is not common to put reducer on discharge side of a centrifugal pump. But I like to know WHAT will happen if I put it? (centrfugal pump/blower).
The similar question could be "What if we put expander on suction side of a centrifugal pump?"
Thanks
I know it is not common to put reducer on discharge side of a centrifugal pump. But I like to know WHAT will happen if I put it? (centrfugal pump/blower).
The similar question could be "What if we put expander on suction side of a centrifugal pump?"
Thanks





RE: Reducer on discharge side of cent. pump
Here is some advice on "Piping terminology"
-Reducer- A device used to change the size of a pipe line from one line size to another line size. No matter which direction the commodity in the line is flowing (in process plant piping) the device is still called a "Reducer." In piping fittings there is no such thing as an "Increaser"or "Expander".
Now, to addressr what I think is your question. (can you put a reducer in the discharge line of a pump?)
Yes! you can put a reducer in the discharge line of a pump. It is done all the time, however it is normally required to change the discharge line from the (smaller) pump discharge size to a larger pipe line size.
I have seen a few (not many) installations where the pump discharge flange is larger than the required line size. In this case a reducer was included just downstream of the pump nozzle.
RE: Reducer on discharge side of cent. pump
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Reducer on discharge side of cent. pump
It is to convert the high velocity flow out of the fan discharge to static pressure.
rmw
RE: Reducer on discharge side of cent. pump
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Reducer on discharge side of cent. pump
Eccentric reducers attached to the suction flange are arranged with the flat side at the bottom when the supply comes from above the pump, and with the flat portion at the top when feeding the pump from below.
RE: Reducer on discharge side of cent. pump
The question above did not ask about the style of reducer (eccentric or concentric) used at pumps. It just asked about the use of a reducer in both the suction and discharge.
Eccentric reducers (when required) should be and will be installed with the flat side up no matter where the suction comes from.
RE: Reducer on discharge side of cent. pump
Pennpiper,
Your last paragraph:
Igor J. Karassik's chapter 12 (Installation, operation, and maintenance), fig 9, in Karassik's et al. Pump Handbook, McGraw-Hill, tells a different story.
Kindly comment.
RE: Reducer on discharge side of cent. pump
It is the way I do it and that is the way I teach other pipers to do it.
RE: Reducer on discharge side of cent. pump
RE: Reducer on discharge side of cent. pump
My own rule is - flat side up if there is entrained air (to prevent air pockets), flat side down if there is silt or solids present (to encourage the solids to be flushed into the pump suction). But if you have a flooded suction with no air and no solids you can install it any way you want, or even use a concentric reducer.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Reducer on discharge side of cent. pump
Artisi and Pennpiper, it is well established that gas pockets (high spots) should be avoided and suction piping should be as short and direct as possible to reduce friction losses, therefore your comments on this subject are understood.
This is a shortened version of what Karassik had to say on the subject (second edition of the Pump Handbook):
The paragraph goes on explaining the arrangement of fittings to avoid flow disturbance.
What's wrong with Karassik's statement ?
RE: Reducer on discharge side of cent. pump
For me the best rule is flat on the top - then you are safe from air collection - however, if there is good reason to change the "rule" to the flat on bottom it becomes an engineering decision where a factors can be reviewed.
RE: Reducer on discharge side of cent. pump
If possible I would prefer to have the vertical section sized to cope with self venting flow, and then the horizontal section either truly horizontal or sloping slightly up to the pump. If there had to be a reducer I would put the flat side at the top. Does Karassik give a reason for wanting it flat side down? Of course, if solids are present then sloping down to the pump would make sense.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Reducer on discharge side of cent. pump
Excluding considerations on air pockets created by pipejoint steps, or by projecting gaskets, it appears that when the size of the suction pipe is larger than the bore of the pump inlet air pockets can be avoided precisely by providing eccentric reducers with the flat side on top.
Sam Yedidiah (Centrifugal Pump User's Guidebook), tells us that when the pipe diameter is more than one size or two larger than the bore of the suction nozzle, a straight pipe section of equal diameter as the pump inlet should be installed between the reducer and the pump because the eccentric reducer may deflect the liquid stream toward one side of the impeller eye, reducing output and efficiency.
From the picture in fig. 9 (in Karassik's manual, chapter 12) one can see that (at the end of the vertical pipe) there is a flanged long-radius elbow, followed by a horizontal eccentric reducer, with its flat portion at the bottom, connecting to the pumps' suction flange (itself an elbow). The arrangement shows a smooth flow profile with no air pocket. Contrarywise, with the flat portion on top, a slope would appear at the bottom, giving rise to more turbulence.
RE: Reducer on discharge side of cent. pump
RE: Reducer on discharge side of cent. pump
The example given by 25362 explains how Karassik justifies putting the flat side down when the feed is from above, or the flat side up when the feed is from below. Does this mean that if the line feeding the pump suction is horizontal and comes from the east that the flat side should be on the west?
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Reducer on discharge side of cent. pump
GUIDELINES FOR PUMP SYSTEM DESIGNERS
Jacques Chaurette p. eng., Fluide Design Inc.
August 2005
Always use an eccentric reducer at the pump suction when a pipe size transition is
required. Put the flat on top when the fluid is coming from below or straight (see next
Figure) and the flat on the bottom when the fluid is coming from the top. This will avoid
an air pocket at the pump suction and allow air to be evacuated.
RE: Reducer on discharge side of cent. pump
My reading of original posting re expander on the suction side was from small to large against the inlet or close to the pump inlet which could be problematic.
RE: Reducer on discharge side of cent. pump
Johnny Pellin
RE: Reducer on discharge side of cent. pump
RE: Reducer on discharge side of cent. pump
Johnny Pellin
RE: Reducer on discharge side of cent. pump
drainability and being able to prove it can be important to the FDA, etc. and if you do it right, it is not an issue for the operation and reliability of the pump (and even if it was, the FDA and Q would not care).
RE: Reducer on discharge side of cent. pump
A jet pump and a multistage barrel pump are very different. A jet pump refers to an ejector, eductor, etc... The pump you are talking about is just a multistage centrifugal pump with double casing same as a boiler feed pump. In boiler feed applications (and condensate pumps for that matter) where the pumped liquid is at or very near saturation. Ask any pump manufacturer, and they will agree with the advice of Karassik. In fact with barrel pumps the manufacturer's preference would be to have a completely vertical drop from the source tank to the suction nozzle.
I2I
RE: Reducer on discharge side of cent. pump
You can have reducers in the discharge(one size, as a thumb rule) but pump manufacturers suggest not to reduce the suction piping below the given suction flange size. So, an expander(I am comfortable with the term expander, technically and semantically, and the term has been in use) is avoidable in the suction line.
RE: Reducer on discharge side of cent. pump
Johnny Pellin
RE: Reducer on discharge side of cent. pump
Moving on to the original question and adding something to satisfy the engineer's desire to have reasons for our rules, let's think about the discharge of a pump. Exiting the pump is a highly turbulent, undeveloped liquid stream. The pump vendor is striving to offer a product that economically meets the specification, and a larger size discharge nozzle = more cost to him. The added cost does not equate to added value beyond the point where excessive wear or reduced product life is avoided. Once out of the pump, however, the engineer seeks the optimum size pipe, which typically would result in lower velocities and pressure drops. Thus the piping is typically larger than the pump discharge nozzle.
Late katmar, I'd almost say that this is ALWAYS the case, but if I did so, I'd violate the points I was making in my first paragraph. ;-)
Doug
RE: Reducer on discharge side of cent. pump
RE: Reducer on discharge side of cent. pump
Step back a minute and think - you're paying for energy to move a liquid at a certain pressure, then by putting in a pipe restriction, you are wasting energy. It's like opening a window in the middle of winter - you're just wasting energy.
There are times when this actually helps, but in general, it's not a logical idea.
RE: Reducer on discharge side of cent. pump
Plus there is no law from the pump police to say that the discharge pipeline must be the same size as the pump discharge flange- pipeline diameter is based on a friction head / economic consideration.
As TenPenny has pointed out "There are times when this actually helps, but in general, it's not a logical idea."
RE: Reducer on discharge side of cent. pump