Pump Suction Line Reducer

No.

No.

what does it mean?

A BRIEF INTRODUCTION TO CENTRIFUGAL PUMPS

Presumably somebody has done some work and decided that suction pipe dia = to pump suction connection is OK (this isn't always the case). In that case it's not easy to fit a reducer

Does the choice of concentric or eccentric reducer depend on suction conditions(positive or negative),velocity of flow at suction or some other factors?.

The concentric is to prevent bubbles of different densities stuck/dam before the eye of the pump.

For normal water - air it must be flat at top.

Oops - finger error - it should have been eccentric

I have never heard of a concentric reducer being recommended in a horizontal pump suction line, but there might be some possible exceptions.

We used concentric reducers in horizontal suction pumps in Saudi Arabia with KSB(German)Pumps but eccentric reducers were used if suction was negative to prevent air trapping.

That sounds unusual, but if it works, it's okay.

Tornado is absolutely correct in regard to his sound advice.

He's earned a GA from me.....

Reducer is not compulsary but it helps in increasing suction velocity of the fluid coming from the bigger dia line and thus improves the suction conditions.

If it is an existing installation and has been operating fine then it is OK. Depending upon the material being pumped and the volume being pumped it quite often cheaper and more expedient to go with a pump of the same size as the inlet piping than to invest in the additional fittings and labor to use a smaller pump. This is not a universal solution but if it works DON'T FIX IT!

This explanation is usually applicable to smaller pumps and not larger ones. This is not intended as an all inclusive answer that fits all applications.

Good Luck, Old Salt

Pumps suction piping are generally kept at larger diameter than pump nozzle size to reduce frictional losses which are dependent on the fluid velocity in the suction piping. But if it happens to be of the same size as suction nozzle then you cannot put a reducer. Just ensure that you have enough NPSHA for the pump to operate with out cavitating.

Once for a duplex water booster set our Sales Engineer selected a common suction line with footvalve and pumps couldn't suck. Later we fitted two separate smaller suction lines and pumps were working properly. The reason was the dia of common suction was too large for a single pump but OK for both pumps sucking together.

I have to agree with gsbasha, instead of reducing the suction side most people need to put a valve in the discharge side and throttle the discharge and prevent cavitation.

The purpose of the reducer is to avoid collection of air in the suction line and thereby obstruct the flow . I have seen it in all horizontal pumps.

hi Irshad,

Pls see the images

please advice

sunil

Good answers but one consideration.

As several people have pointed out, the suction line is typically sized larger than the pump suction to provide a small loss on the suction side of the pump so you have adequate NPSHa but the orientation of the reducer depends on the service.

If you have water (or some other clear liquid) you need to put the flat side of the eccentric reducer on top but if you are pumping a slurry you should put the flat side on the bottom to prevent the solids from accumulating and possible plugging the suction line.

What fluid, at what temperature and pressure?

There must be the correct conditions at the inlet of the pump, otherwise cavitation and pump damage will ensue.

HI,

I thing all the details i have provided

fluid = water

pressure and temperature mentioned in the images

sunil

Here suction pressure you gave 6.5 barg but design data for pump at #17 it is 0 psig with differential head of 45 m. So please check whether pump seals are properly designed for 6.5 barg suction pressure. You have not commented question from many members about orientation of the pump, horizontal or vertical and pump is installed or yet to be installed. The engineering firm who has designed piping cofiguration and sizing should be questiond whether suction velocity (appears to be high) is considered as per relevant standards while deciding the suction pipe size.

hi,

pumping temperature is 28 deg c reated

52 deg c max temp

28 deg c norm

12 deg c min

sunil

OK. Nothing too arduous.

Now, what is the size of the pump inlet and what is the size of the pipe that it is to be connected to?

_{Here we are 20-odd posts in, and the full information about this installation is still being uncovered....}

hi,

pump suction nozzle size is 8" dia

and the lline size is also 8"

sunil

Then there's no scope to install a reducer!

_{<mutter, mutter...>}

Your line size is 8 inch and pump suction is also 8 inch then where is need of reducer? and why this question was raised? Do you face some problem in your pump?

It is unlikely the problem is to be found in the pump....

hi,

Appreciate the comments but, who will see the suction velocity, cavitation & air bubbles

what will be the pump performance sue to this

can u give me the guarantee pump life.

i am not a fool to ask u

sunil

The pump manufacturer should be approached for commercial warranty issues.

If the suction line is inappropriately sized, then everyone will see cavitation!

"cavitation" is always due to lack of feed volume inducing a vacuum.

It sounds to me what you need is a 10 or 12" line, or you need to pressurize the the feed reservoir. Or as mentioned, throttle the output.

Then, if you went for a larger line, you would put in a reducer to 8" at the pump so the things join up.

GA, with a possible addition. Many pump manufacturers recommend a straight piece of pipe, length 6 x pipe diameter, with no fittings, entering the pump suction. On this basis, any reducer would be a short distance from the pump rather than attached directly.

Good point. GA back at you.

Turbulence and/or a large velocity gradient, right at the intake, is not preferred.

Also meaning any bends involved should be in the (even) larger feed line, not in the intake run.

Will you quote from any manufacturer as well as its name?. Is it for a particular type of pump or in general to all types of pumps?.In saudi arabia we installed reducer directly to suction and discharge flanges. The sales engineers never calculated NSPH but referred some charts or tables.For flow meters I have heard that there should be a minimum length(xD) of pipe without fittings on either side.We get knowledge from many sources like text books,Engineer's reference/hand books, manufacturer's catalog,codes/standards,own experience, experienced people in work places as well as from Engineer's forum. Do they contradict with each other?.

All centrifugal pumps.

He's already told us in #20 that the suction pressure is a massive 6.5 barg.

Suction velocity is about 2.5 m/s, depending on pipe schedule, which might be a bit brisk if the suction system were marginal, but with 6.5barg at the pump it's OK.

I've known of multi-stage pumps for seawater injection for secondary recovery on oil platforms, typically 2500kW with 200bar ΔP, and they only needed a suction pressure of 5barg, provided by an "ordinary" centrif. 4.4bar ΔP here is hardly in that league!

You are feeding data and then asking guarantee for the pump performance ???

Many contributers have suggested to put all the details in one go so that appropriate suggestions can be contributed. You said that you are not fool to ask the question, but contributors can suggest based on you data, your main line is of 8 inch and pump suction is also of 8 inch dia then where you are suggesting to put the reducer. I may not be understanding your requirement, but as the subject is broad, and replies can be in particular direction, you should come up to put the exact problem in the forum with all the details available.

Good luck.

As you've given a figure for NPSHA, suction line losses must have been calculated. With 76.1m NPSHA it's most unlikely there will be a cavitation problem. NPSHR probably less than 1/10 of that.

I would specify a mechanical seal as 6.5 barg suction pressure could cause excessive leakage from a packed gland.

Now, what is the length of the suction line?

And what is the suction pressure (the static head)?

GA.....you forgot to mention the inclusion of photos and/or drawings.

Great answer above. Sometimes it requires a lot of information to get to the specific issue.