Sewege Transfer Pump - Rotary Lobe Type
Sewege Transfer Pump - Rotary Lobe Type
(OP)
In one of the jobs I have to specify a pump for domestic sewage transfer to waste water treatment plant. The Pump Flow is 290 USGPM and Required Head is 230 ft. The pump will take suction from an above ground Sewage Tank.
Here in Saudi Arabia, typically centrifugal non clog type impeller pumps are used for this service.
But due the required duty point specified above the centrifugal type of pump is not available in the market.
Second choice is to go for rotary lobe type of pump.
Is anybody familiar with use of rotary lobe pump in domestic sewege transfer?
Is it good in this service?
Does it require some kind of inlet protection i-e grinding or screening?
What is the maximum particle size it can pass?
Thanks and Regards
Here in Saudi Arabia, typically centrifugal non clog type impeller pumps are used for this service.
But due the required duty point specified above the centrifugal type of pump is not available in the market.
Second choice is to go for rotary lobe type of pump.
Is anybody familiar with use of rotary lobe pump in domestic sewege transfer?
Is it good in this service?
Does it require some kind of inlet protection i-e grinding or screening?
What is the maximum particle size it can pass?
Thanks and Regards





RE: Sewege Transfer Pump - Rotary Lobe Type
RE: Sewege Transfer Pump - Rotary Lobe Type
Wet pit submersible sewage pumps also tend to be expensive to operate and maintain. Dry pit pumps are preferred by many lift station operators.
Why don't you look at another centrifugal pump? For example, KSB makes a pump for this application. KSB calls it the Sewatec:
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RE: Sewege Transfer Pump - Rotary Lobe Type
RE: Sewege Transfer Pump - Rotary Lobe Type
I would think that the 0.59" solids handling without a grinder/macerator would preclude it as a raw sewage pump.
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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
Bimr,
The pump selection that you have provided shows pump is running close to its runout condition OR we can say end of curve operation.
Centrifugal Pump operation at runout conditions should be avoided.
Same is true for pump operation near shutoff conditions.
Actually this is the problem in selection of centrifugal non-clog impeller type pump for this service (290 USGPM, 230 FT). Some of the big names in sewage transfer has refused to offer a centrifugal pump for this service. These include Grundfos, Flowserve, Saudi Pump Factory etc. And if the Vendor do offer a pump, the pump is operating near the shutoff or at the runout condition.
On the other hand there are some pump manufacturing companies like BORGER Germany and NETZSCH USA who offer rotary lobe pump for this service. They claim that solid content of upto 50mm dia can be passed. Please look at the following links for Rotary Lobe Type Pumps is Sewage Transfer service.
http://www.boerger.com/contero/boerger_535_.html
http://www.netzschusa.com/tornado.htm
I am in contact with these Vendors and hopefully will get answer.
My questions are:
Is anybody familiar with use of rotary lobe pump in domestic sewege transfer?
Is it good in this service?
Does it require some kind of inlet protection i-e grinding or screening?
Regards...
RE: Sewege Transfer Pump - Rotary Lobe Type
First up, I don't think that bimr needs a lesson in pump hydraulics, especially when he is only passing on a pump selection made by KSB.
However,I wouldn't use this pump for reasons other than its operating point;
1: 2 pole speed
2: limited solids handling
What ever pump you use I think that grinding will be needed.
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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
@Bimr
I sincerely apologize for any unintentional teaching as pointed out by Artisi. I was only describing the difficulties I am facing in selection of centrifugal type of pumps.
Regards
RE: Sewege Transfer Pump - Rotary Lobe Type
What you are facing is normal for such a duty, low flow / high head dicates a narrow but large diameter impeller not suitable for sewage / solids handling. Therefore you need to make an informed decision of operating at other than the best hydraulic point on the curve. For solids handling it is usually to the left so that larger solids can be handled (larger pump) or else use a different pump than centrifugal.
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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
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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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
If you can't find a centrifugal pump, look for a peristaltic or a diaphragm pump. At least the diaphragm pump can handle long and big particles.
RE: Sewege Transfer Pump - Rotary Lobe Type
RE: Sewege Transfer Pump - Rotary Lobe Type
One option which I failed to mention is to use two pumps in series. Use one submersible and one vertical centrifugal.
However, the best solution is probably the Gorman Rupp Ultramate pump. It has two pump in one assembly, with a centrifugal pump mounted above a suction lift pump and driven by one motor.
http://www.grpumps.com/upload/AV-05796.pdf
Regarding Artisi's slurry pump selection; it is an elegant solution looking for a problem. You probably can not afford it. It will probably require a 3600 rpm as well.
Regarding the KSB pump selection above; the pump selection was made using the online pump selector. The pump selection should be made by the pump manufacturer. The online selector proposed a sewage pump, however, the online pump selector proposed a poor fit for the application.
I agree that it is best to avoid 3600 RPM motors and pumps.
RE: Sewege Transfer Pump - Rotary Lobe Type
RE: Sewege Transfer Pump - Rotary Lobe Type
The Gorman Rupp, now that is an elegant solution.
The Goulds CWX will run 1800RPM - I no longer have curves for these pumps but maybe it will hit the duty with 1500rpm. But you are correct the up-front costs it will be expensive however, keep the bearings oiled and the gland packing in good order and it will last for 50+ years on this application.
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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
Operating so far to the left of the BEP imposes force loads on the shaft. These unbalanced loads cause shaft deflection, vibration and premature bearing and seal failure leading to pump failure.
RE: Sewege Transfer Pump - Rotary Lobe Type
RE: Sewege Transfer Pump - Rotary Lobe Type
A couple of comments just for the records.
The 5x4x17 CW pump is on the No2 bearing frame with is capable of handling a many hundreds of HP and is used on all 17" impeller units upto and including 12x10x17, the load/shaft deflection from the 5x4x17 duty would be meaningless in comparison to the shaft capabilities and the bearing life would be into the millions of hours.
Having been involved with A-C pumps (now Goulds) for over 20 years I have never seem a bearing or shaft failure (on the CW pump and its sister PWO) due to poor application, discounting things like lack of lubrication, water ingress etc. I've seen the casing pushed from the bearing housing and burst Fenner Dodge rigid couplings due to wrong rotation, the shafts and bearings usually survived.
Yes, in hydraulical terms not very efficient however, in terms of reliablity and life etc it is 100% efficient. Having an 85% efficient pump constantly down for maintainance, repairs and replacement parts, clean out of blockages etc, is really not all that efficient.
If I was the engineer on this project I would have confidence in putting this unit forward for serious consideration.
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.)
RE: Sewege Transfer Pump - Rotary Lobe Type
The CW and CWX pumps will work for a hundred years but it will take that long for payout as they are EXTREMELY expensive, and with the breakup of ITT, very questionable manufacturing point. This is an industrial slurry pump using hardened chrome internals and priced accordingly.
My son works for Goulds and says the CW/CWX will be now coming out of Seneca Falls; not the old AC plant. That is, once they get their crap together; which may be a year or two. With patterns, drawings, and engineering files scattered all over the place, this will be priced as a "replacement pump"; which in the pump world means "triple the price".
RE: Sewege Transfer Pump - Rotary Lobe Type
Progressive cavity pump also have a long barrel which make this type of pump very difficult to fit into a lift station. The cost of the lift station structure will be expensive for a progressive cavity pump.
I work in the environmental field and have never seen a progressive cavity pump in service in a lift station pumping application.
RE: Sewege Transfer Pump - Rotary Lobe Type
PC pumps get the nod many times as a result of being the only solution remaining; ergo, they get a lot of DOG services thrown at them.
I would first look at a dry-pit non-clog centrifugal here, but the head is too high for an economic solution with a centrifugal. Then in the PD pump family, I would consider a PC pump first over the other rotary type PD pumps: gear, lobe, etc.
They are very well suited to hard angular solids (which give trouble to gear/lobes) as the stator has the ability to conform to the solid's shape and "roll" them through the pump without much abrasion. Long stringy solids should be chopped by macerator/grinder; which needs to be a part of any PD pump package.
The PC pump, if sized properly, runs relatively slow and has a very high reliability. The gotchas with a PC are allowing it to run dry, which can tear up the stator in no time; and using the wrong rotor/stator materials. Natural rubber is the very best material we know of in terms of combating abrasion; it is not however very tolerant of hydrocarbons and other petroleum based oils. If they are present, go to a nitrile or Buna rubber.
If the rotor/stator is properly selected and kept wet, then the next thing to look at is the mechanism that translates the driver's concentric rotation into the elliptic motion of the rotor. This is sually acheived by some sort of geared universal joint. The very reputable vendors (Moyno, Netzsch, Mono(now NOV Mono?), all provide high quaility drive trains and these can make the PC the very lowest Total Life Cycle cost solutions in high solids service.
Would like to see a cost comparison among some of the several solutions we have talked about; remembering that this is tough duty on ANY type of pump. Its just a matter of finding the pump that will fail the least often.
RE: Sewege Transfer Pump - Rotary Lobe Type
Actually the "Big" Oil and Gas Company in Saudi Arabia has very stringent guidelines for Centrifugal Pumps. It has to operate within 60% to 110% of BEP envelope, otherwise it is technically not acceptable. My first choice for this service was a centrifugal non-clog type pump but as explained above in this thread there is no pump in the market which falls in 60% to 110% BEP criteria.
So I have to go for a PD Pump and most common PD Pumps in market for sewage service are Rotary Lobe Type and PC Type. Thats why I asked in this thread whether somebody has an experience in using Rotary Lobe Pumps in Sewage Transfer.
Now based on all the discussion in this thread following can be conlcuded.
1. Rotary Lobe Type Pump can be used in this service.
2. It will have maintenance issues relating to fibers and solids in the sewage. But this pump will take suction from a Pre-aeration Tank which is above ground and will allow some solids settling time. Anyways, I will consider installing an inline grinder upstream of the pump to safeguard the pump.
3. Dry run protection will be required which can be offered by the pump Vendors.
4. Upgraded pump materials will be used with proven experience in Sewage Transfer.
Once again Thanks to everybody for their kind interest in this issue and providing me with their valuable knowledge.
Regards,
Haroon
RE: Sewege Transfer Pump - Rotary Lobe Type
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.)