Help with shaft seal options for water pump application

[fastline12]

We are working on a small water pump application. The internal pump pressures should not exceed 100psi and likely much less than that. We are trying to find the most economical route to selecting and sourcing seals. We want to use off the shelf sealed radial ball bearings between the shaft and housing but need to seal out water from coming in contact with the bearing. From my experience, some type of mechanical seal should work here but I certainly do not want to over design this and blow the budget. I doubt a simple lip seal will get this done though.


Ideas? Shaft speed not to exceed 2000rpm, pressure not to exceed 100psi. pumping potable water only.

 

[MikeHalloran]

A properly selected, designed, lubricated, and installed o-ring would be my first choice for 'economical'.

You still need a vent and a drain between the seal and the bearing to drain away whatever gets through the seal, regardless of what you use for a seal.



Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Mechanical seals are used on most pumps.

http://www.mcmaster.com/#mechanical-seals/=nr0kwd

 

[rotw]

To my knowledge the most economical is a packing ring.
Is that what you mean Mike Halloran?

According to KSB, this solution is recommended for :

- Constant Suction pressure (allowed variation +/-2.5 bar)
- Constant temperature (+/- 10 degree C)
- Constant speed (+/-4%)
- Continuous service (non intermittent)
- Clean process fluid
- Sufficient leakage rate

 

[rotw]

Gland packing I Meant (sorry I have to translate from French what is known as Garniture presse-etoupe)

 

[1gibson]

Packing and a flinger* on the shaft.

* = pretty much what it sounds like; some sort of collar on the shaft that prevents direct spray of water from the packing to the bearing, and will fling off any water that hits it, preventing it from travelling across the shaft to the bearing.

 

[fastline12]

I want to confirm that the "gland" you are talking about is an Oring? Basically a a radius groove machined around the circumference of the shaft? There would be no way to lubricate that if that is the consideration.


Regarding leakage of seals, there is not much in the design to deal with leakage but in my experience with mechanical seals, they should not leak? I know most pumps have weep holes to indicate the seals are failing and not fill the the bearings with water but I have not seen one leak constantly when operating correctly. Is that typical of higher pressure pumps? I guess the ones I am thinking of are 60psi or less.

 

[Tmoose]

how many hours is this supposed to last?

 

[amorrison]

There is a pump group at forum407

 

[MikeHalloran]

It would probably be better to put the o-ring in the housing and leave the shaft without a notch. The o-ring is greased at installation. This can be satisfactory if the rpm is not too high. It's not as simple as just cutting a groove and slapping a ring in. Download Parker's O-Ring Handbook and study it.

A mechanical seal will generally give a longer life than an o-ring, but costs quite a bit more. Neither lasts forever. In between is a Bal-Seal, which fits in an o-ring groove.



Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

A cross section drawing of your pump would help as I think your description is a little vague as to what exactly you have / want etc, however in the interim - look at SKF V ring seals.

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.)

 

[cjccmc]

I was involved on an R&D project similar to the application you describe several years ago, same in that fluid was potable water at 100 psi. Test speed 200 rpm on 1.5" dia shaft. Program involved finding a seal that could last 10 years without maint. We tried multiple types, best only lasted 1 year but we had a very low leakage allowance. Some points:

Shaft dia matters a lot at 2000 rpm. Larger dia means more wear and heat.
There is a type of plastic seal where water acts as lubricant but cant go above 150F
Parker advised that an O-ring in dynamic application at our speed and pressure would not last very long. Based on that input we dropped O-rings from the test.
Lip seals using reinforced plastic (e.g. PTFE with carbon) last much longer than non-reinforced but eat thru the shaft (need hard shaft coating)
Lubrication adds a lot of life to a plastic lip seal.
Mech seal results were very dependent on the quality of the seal mfg. More elite and expensive firms had better results.