Pump...suction 1-1/4"...outlet 1"

[chownah]

I got a good deal on a Super Pump...which is evidentally made by Mitsushita. It has a 1-1/4" suction and a 1" outlet. The pipe coming from my well is 1" so I put a reducer fitting right at the pump suction inlet to reduce to 1" to match the plumbing from the well. I can't really see that this will have a serious negative effect....it will of course increase power consumption a tiny bit but I can't see that it will cause premature failure of the pump....do you think?

Chownah

[Crossy]

Shamelessly plagarised from here :- http://www.eng-tips.com/viewthread.cfm?qid...254&page=10 talks about 'real' pumps (6" inlets) so I don't know how much applies to our baby pumps, interesting reading none the less

"Pumping Station Design" Copyyright 1998 Butterworth Heineman (A member of the Reed Elsevier group)

Page 645 (Section 22.2 - Avoiding Vibration Problems) - "Pump Suction Piping - If possible, use straight suction piping up to the pump suction nozzle, and keep any required bends in a single plane. As a minimum, avoid piping reducers or bends within 5 to 10 suction pipe diameters of the pump inlet, unless the pump has been specially designed to accommodate such fittings closer to the pump (as in some vertical nonclog pumps). If in doubt, seek the manufacturer's advice."

Page 646 - "Net Positive Suction Head - To minimize hydraulic forces for all types of pumps, it

is important to operate the pump with sufficient NPSHA

(see Section 10-4). In addition to causing cavitation,

inadequate NPSHA can excite unexpectedly high vibrations

at various natural frequencies. From Bernoulli's

equation, any increase in local velocity decreases static

pressure and thus increases the cavitation potential, so

it is important to keep the pump inlet flow velocities

low (preferably below about 2 m/s or 6 ft/s) and evenly

distributed. Hence, a large suction pipe (at least equal to

the pump suction flange ID) should be used. Pipe

reducers should preferably be at least five pipe diameters

upstream of the pump flange. Maintaining this distance

from more aggressive suction disturbances such

as valves and elbows is even more important. Besides

avoiding cavitation, this practice also ensures well-distributed flow velocity and pressure at the inlet and

throughout the pump, and thus minimizes the hydraulic

excitations in general. High velocity in the discharge is not usually important because the pump increases the

static pressure well above the cavitation point."

=====================================

[tutsiwarrior]

Shamelessly plagarised from here :- http://www.eng-tips.com/viewthread.cfm?qid...254&page=10 talks about 'real' pumps (6" inlets) so I don't know how much applies to our baby pumps, interesting reading none the less

"Pumping Station Design" Copyyright 1998 Butterworth Heineman (A member of the Reed Elsevier group)

Page 645 (Section 22.2 - Avoiding Vibration Problems) - "Pump Suction Piping - If possible, use straight suction piping up to the pump suction nozzle, and keep any required bends in a single plane. As a minimum, avoid piping reducers or bends within 5 to 10 suction pipe diameters of the pump inlet, unless the pump has been specially designed to accommodate such fittings closer to the pump (as in some vertical nonclog pumps). If in doubt, seek the manufacturer's advice."

Page 646 - "Net Positive Suction Head - To minimize hydraulic forces for all types of pumps, it

is important to operate the pump with sufficient NPSHA

(see Section 10-4). In addition to causing cavitation,

inadequate NPSHA can excite unexpectedly high vibrations

at various natural frequencies. From Bernoulli's

equation, any increase in local velocity decreases static

pressure and thus increases the cavitation potential, so

it is important to keep the pump inlet flow velocities

low (preferably below about 2 m/s or 6 ft/s) and evenly

distributed. Hence, a large suction pipe (at least equal to

the pump suction flange ID) should be used. Pipe

reducers should preferably be at least five pipe diameters

upstream of the pump flange. Maintaining this distance

from more aggressive suction disturbances such

as valves and elbows is even more important. Besides

avoiding cavitation, this practice also ensures well-distributed flow velocity and pressure at the inlet and

throughout the pump, and thus minimizes the hydraulic

excitations in general. High velocity in the discharge is not usually important because the pump increases the

static pressure well above the cavitation point."

=====================================

this is all true...the larger suction diameter is there for various reasons and the pump manufacturer would expect the purchaser to follow the usual practice with the installation otherwise you eat up yer impeller with cavitation an' that ain't the pump vendor's fault...

in a large industrial application if ye messed about widde usual suction arrangement the pump vendor would void the warranty...suction piping design (supports, layout, etc) incorporate these considerations...a reducer next to the pump suction flange is clazy...

(although ye get the odd expansion joint/compensator on the suction side that increases turbulence but not de fluid velocity...)

Edited March 8, 2007 by tutsiwarrior

[chownah]

Thanks for the advice guys. Indeed the pump is running with quite a bit of noise. One of my wife's friends has the same type of pump and she says it makes noise the same as ours....she has been using it for a long time so I the noise itself does not spell immediate doom...I guess. I'm debating whether to replumb the suction inlet piping or just forget it.....I'm also considering going with a smaller pump since this one is 1-1/2 horsepower and dims the lights noticeably more than the previous 1 horse pump we replaced.

Anyway thanks again for the input and the link was really interesting.

Chownah

[ProThaiExpat]

I share your concern, but my concern is on the outlet size. My outlet pipe from the pump appears to be one and a quarter or more and my house plumbing is 1/2 inch.

While the reduction in the piping increases pressure it also makes the pump work harder and since I have had the pump for five years and have replaced the pressure regulator or manifold, or manifold pressure releif valve almost every year, I am sure my pump is just too big for my installation. My neighbor has a much smaller pump and it works fine.

When and if my big pump finally calls it quits, I will replace it with a smaller pump, but in the interim, calling out the service people once a year and paying about 800 baht for the service seems the most economical way to go.

You might consider a similar approach and be happy it works now and deal with it when something goes amiss.

[Gary A]

I'd buy the smaller pump and save electricity. Why use a bigger pump when you get no benefit from it?

[steve73]

Chownah,

If you restrict the outlet a little, it should reduce the cavitation. It will also reduce the power requirement slightly. but it does depend on what the pump is used for. It its for topping up a header tank, it'll take longer to fill. If its to supply small users (taps, faucets, washing machines, showers, etc, then they should provide enough resitance so there'll be little benefit in restricting at the outlet.

and yes, a bit longer full bore inlet section with no bends will help a little, but it really depends on how low you're pulling the water from.

PTE,

you could run a small recycle back to the suction side, and this would save your pressure regulator & relief valve. Don't make it too big or it'll reduce the supply pressure too much, and could overheat the pump. Oh, and the recycle will increase power consumption a little.

Steve,

(Process engineer, oil & gas production, but small pumps behave exactly the same way...)

[rken]

Dont get to anul.

No problem. Should not cause a problem in the life of the pump. But as one poster pointed out it might be more pump than you need. Depends on your system as to its ecomonics. Many systems have a pressure tank that store presurized water and keeps your pump from cycling on and off rapidly witch increases power consumption. If you have a good pressure tank system then the larger pump will not be a problem. But I don't know your system and your pressure and volume needs. So go with what you got and I think you will have no problems

[Lickey]

Interesting topic gentlemen, let me give you some details of the borehole system on wifes farm and can you confirm or deny my suspicions please, its a 1.5 hp submersible down 25 mtrs, it has a steel 1,1/2 elbow outlet on the top, it then goes into 2inch blue for near 200mtrs uphill with 1inch outlets for a sprinkler onto papaya, problem is it works fine for 30secs, then just dribbles for a min or so, then gets going again, in the "dribble" period, it dosent spit or fart so to speak which would suggest to me that the water table is still good and not pumping air, also when i water the salad garden through the black plastic cover, i need a good jet of water, this is only possibble if i block of pipe for 30 secs, then i get a really good jet for a min or so, the pump has been in borehole for about 18 months now, although perfomance has deteriated in this time, is it need of a clean and service ect? thanks for any tips and advice, lickey..

[Lickey]

I know my previous post is more for the farming forum, although ive read every post on irrigation and boreholes ect, but this one is the only one ive seen concerning pipe size, am i right in thinking that the outlet side should be slighty smaller than the inlet, so as to maintain pressure, thanks for any help you can give me, Lickey.

[chownah]

I know my previous post is more for the farming forum, although ive read every post on irrigation and boreholes ect, but this one is the only one ive seen concerning pipe size, am i right in thinking that the outlet side should be slighty smaller than the inlet, so as to maintain pressure, thanks for any help you can give me, Lickey.

Inlets are quite often bigger than outlets but not for the reason you have stated. Larger inlet sizes are to reduce water velocity in the suction pipe so that turbulance is reduced and so that resistence to flow is small. You don't want turbulance in the water entering the pump because this will increase the chances of cavitation which reduces efficiency and increases wear on the pump impellor. You want to minimize flow resistence because the more flow resistence you have the lower the pressure will be at the pump inlet and this lower pressure will increase the chances of cavitation which is unwanted for the same reasons as given above. Another consideration for a large pipe diameter at the inlet for centrifugal pumps (the vast vast majority of pumps used in domestic water systems are centrifugal pumps and alot of those used for irrigation are too) is that the water must make an approximately 90^o bend upon entering and if this bend is made tighter or with higher water velocities then it increases the chances of cavitation which is unwanted for the same reasons given above and generally speaking having a larger diameter inlet pipe can both smooth out the bend and also decrease the velocity at entry.

There may be other reasons that I don't know about but I don't know about those so haven't listed them here....hahhahahha

Outlets are sized to match typical pipe diametres, flow rates and pressures required for various applications...also sizing balances the cost of the pipe with the benefits obtained (less energy consumed in pumping, comfortable pressure in the shower) for a particular type of application. I'm probably leaving a lot of stuff out here too!!!

Chownah

[Lickey]

Thanks Chownah, your reply that all should be ok with pipe sizes ect gave me a different line of thought, perhaps the outlet pipe had got silted up over the months, I cut through the 2" near the pump and the water flowed back from the hilltop big time, got soaked cutting pipe!!, then turned pump on to check delivery, water came out in fits and starts, 10gals min then nothing for a min or so, so its low water or stones i presume, will pull out next week and check pump, thanks again,

Lickey..