Does anyone have experience with rebuilding a pump? We're considering that as an alternative to new

[pa5tabear]

I haven't yet gotten cost quotes, but what does everyone think about rebuilding a pump instead of purchasing a new one? Can we expect like new performance and reliability out of it? We'd be going to a professional pump rebuilder.

I don't know what the condition of our current pumps is, just that they output 100-200 psig below their pump curve pressures.

 

[ash9144]

You don't give a lot of details but strictly speaking rebuilding is far more common than replacing. Normally you would rebuild just replacing whatever parts were damaged or worn. Just as a first guess it sounds like you need a new impeller.

 

[DubMac]

Please don't be lazy; take the time to provide a little detail if you want a substantive answer. Having zero detail, the big picture answer is to compare the cost of rebuiling/ year to the cost of a new pump/(avg life in years).

If you have a swimming pool pump that costs $400, replace it every time. If you have Cat-Cracker bottoms pump that costs $500K, rebuild it every time. I fit falls somewhere in between, then apply the above formula.

Generally a loss in pressure is due to your running clearances opening up due to wear; that is, the wear rings between the pump case and impeller. This causes a portion of the high pressure fluid exiting the impeller discharge to slip back into the suction side of the pump through those clearances. This results in wasted power, increased erosion, and some other crap that you don't want happening. These open clearances could be caused themselves by other things, such as bearings wearing out, imbalance, running the pump at a bad place on the curve.

If you would provide more detail on the pump you have, the service it is in, etc. some of the pros on this site can assist you with some very detailed info on your next step with regard to repair/replce options. Please don't expect detailed and informative answers to general and blurry questions. Sorry if this is offensive to you; but I am a grouchy old man.

 

[micalbrch]

Pretty often the money for rebuilding (repair) a machine is another pocket than purchasing a new machine. I did see it often in the past that customers repaired a pump although a new one was just slightly more expensive. The reason was that one pocket was "operation costs" while the other was "capital spending" and that one was hard to get approved. Of course it is the same amount of money but...

 

[LittleInch]

You should be able to get "as original" performence, but also don't forget to see what a brand new pump can give you in terms of efficiency and hence less OPEX and power costs. As you quote 100- 200 psi less it sounds like a fairly decent sized unit. a difference of 5% efficiency add up to a hell of a lot at todays power costs compared to what it cost 15 to 20 years ago..., not to mention increased motor efficiency over that time.

Dub mac is right though - a vague question = a vague answer. Your call.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[1gibson]

Is "like new" performance really ideal, or are the original pumps oversized, and now having data from XX years of operation, you could spec a new pump that is better suited to your system? If you hit the nail on the head when sizing the original pump, then just compare costs. But if you didn't, factor in potential energy savings as an advantage for a new unit. To be fair, those savings could also be had if you trimmed impellers during a repair. Being 200 psi low seems like it only bothers you a little bit, so I'd guess the pumps are pretty well oversized and even trimming the original impellers still might not be a great fit.

 

[pa5tabear]

I realized our current pumps may meet our needs. I thought we could use a VFD to scale down flow but the lower flow curves do not have sufficient pressure (we are shooting for 600 psi/ 1380 head-ft).

Our pumps are RotoJet RGB III 2x2. Rated at 60 gpm and 2370 head-ft. I don't yet know the original cost or rebuild cost. Pump curve linked here:

http://imgur.com/vWsyztA

@1gibson: We want a VFD system, because yes, they are oversized for the majority of use. The pumps in question are used in our high pressure water system. The draw on the pumps is mostly low (~20 gpm) when a few hoses are used, but we want it capable of high capacity (~120 gpm) for when the full cleaning crew is on site. The 200 psi low is not such a problem when just a few hoses are used, but is a major problem when more people/hoses use the system.

@LittleInch: Yes, I know this is significant, and I'm trying to figure out the best energy solution for us. Mostly we are low flow, but the pump has to be capable of putting out high flow, and we want high pressure regardless of flow.

 

[1gibson]

If you have multiple pumps, and a long period of operating experience, you might be better off looking into operating X number of pumps at a time based on demand (auto start with low pressure switch?) rather than VFD all of the pumps all the time. How many pumps do you have in parallel? Or by "pumps" do you mean there are multiple, individual installations of 1 pump each? What's the cost of one additional "standby for high demand / installed spare" pump versus cost of adding VFD's?

If you want "high pressure regardless of flow" then you do not want VFD's on centrifugal pumps. VFD will lower pressure by the ^2 of RPM change, and head by the direct ratio of RPM change. This usually means that 1 big pump can't provide the required pressure at very low speed (as you have mentioned above.)

 

[Artisi]

What are the alternatives - none - just base it on repair costs versus new pump cost.

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.)

 

[LittleInch]

Looking at your pump curve and your "normal" flow vs full flow, not to mention you shoot for 1380ft, but have a pump apparently capable of 2400, I'm with 1 Gibson and what you need is more or different sized parallel pumps properly sized and working at our close to their BEP. Not sure why you just can't speed up the VFD to get your pressure up at low flow though....

So my thoughts are for you to work out for how long you need different flows, get a new efficient pump for your flow which occurs the majority of the time then add additional pumps to get your max flow which occurs "occasionally". Don't forget vfds have significant additional losses when looking at power costs.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JJPellin]

RotoJet pumps are designed to have a substantial down-turn. This is a pitot tube pump. The loss in performance is likely due to wear on the pitot tube. This can be easily replaced at low cost and performance should be restored.

You should evaluate your service. This pump is not going to perform well in a service with abrasive solids. It acts like a centrifuge, concentrating the solids in the rotor until they build up to the level to grind off the end of the pitot tube. You could try a pitot tube made of a harder material or coated to resist the erosion. But, ultimately, this pump type is not well suited to services with heavy solids present.


Johnny Pellin