Bellows after pump discharge
Bellows after pump discharge
(OP)
Dear Colleagues,
My boss keep telling that there shouldn't be any bellows after pump discharge. He says there are a basic rule stating that we can not put bellows right after the discharge and inducer.
Thanks,
Cheers
MW
My boss keep telling that there shouldn't be any bellows after pump discharge. He says there are a basic rule stating that we can not put bellows right after the discharge and inducer.
Thanks,
Cheers
MW





RE: Bellows after pump discharge
I guess the most fundamental rule for applying these things would be, make sure you really need them, because they're just one more thing that can go wrong if not done properly.
RE: Bellows after pump discharge
I can't add anything of worth to Scipio's valued comments and recommendations except that it is my personal experience that what he states is engineering reality: the flexing and cycles that a bellows joint undergoes in some services will take it to the destructive failure mode eventually - something that you may not be able to control or tolerate.
You haven't identified your reason for employing them in the first place. You, as an engineer, have to have a solid and serious reason for using them; is it because of misalignment, vibration, flexing, thermal expansion, etc.? For whatever the reason, I still (like Scipio) would strongly advise against their use - especicially if the contained fluid is hazardous or can cause a safety problem if allowed to leak or spill. I have used them with success and with failure(s) as well. I would not venture to use them on an application without experienced, knowledgeable, and trusted pipefitters and millwrights involved in the actual installation and startup.
Even if you succeed in a good installation and application; you still have to maintain a strict operating log and inspection routine on the bellows if you want to go home and relax without any worries. They require serious and strict maintenance on a regular and controlled basis. Then, also, there is the question of using the correct metal or alloy as well as the correct mechanical design and fabrication in order to avoid built-in stresses at each fabricated bend. I hope by now you can appreciate what your boss is trying to tell you.....
I hope this experience is of some help.
Art Montemayor
Spring, TX
RE: Bellows after pump discharge
In both cases, the vibration engineers recommended hard solid fastening at all times.
Measures such as bellows were recommended only if there was a problem, and each case would then be analyzed and solved as a distinct case not applicable to other cases. In other words, if you need some sort of vibration alleviation on one system, do not make that a rule on all future installations.
PUMPDESIGNER
RE: Bellows after pump discharge
My opinion is that short of having a specific reason for putting a bellows, as mentioned by Montemayor, you are better off just doing a good job of designing and supporting your connecting piping so that it does not impose any loads on your pump, rather than depending on bellows to cover sins in the design phase.
While I have seen my share of them, I have seen many more pumps without them than with them.
rmw
RE: Bellows after pump discharge
The reason is that in many cases there is no problem allowing the pump to support piping in specific cases, on small pumps it is done all the time. But then no one is looking at that to see if it is correct, assumptions are made (presumptions really), then a problem occurs.
PUMPDESIGNER
RE: Bellows after pump discharge
Where piping is run by "plumbers" you will find the ubitiquous rubber bellows either side of a pump. To get them to put tie rods on the discharge unit to prevent loading the pump from the pressure thrust is like asking for gold.
There is absolutely no need for them unless there is a thermal case to design for. If the piping is a thermoplastic material then there well may be a need if the piping layout doesnt facilitate the use of elbows to take up strain. As most "plumbers" install PE/PP/ABS like steel or ductile iron piping they have ended up with bellows.
RE: Bellows after pump discharge
My input to this discussion is to highlight the fact that extremely high axial thrust from the expansion bellows can be applied to the pump casing.
Be warned.
International College
Naresuan University
Phitsanulok
Thailand
RE: Bellows after pump discharge
At our plant we found that one application had high vibration transmitted from the piping to the pumps, causing false brinneling of the bearings. Expansion joints were the solution to this particular problem.
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RE: Bellows after pump discharge
International College
Naresuan University
Phitsanulok
Thailand
RE: Bellows after pump discharge
International College
Naresuan University
Phitsanulok
Thailand
RE: Bellows after pump discharge
If the reason is thermal expansion, is it right enough? The problem happened in thermal oil pumps in our boilers. Our pumps' mechseal and bearing fail too shortly. It is not misalignment case, because we recheck the alignment in hot temperature. It's OK.
The pump size is 100-250. Yeah, until my boss notice the bellows. What is the indication if our pumps suffer pressure thrust from bellows? The volute casing is not broken. If mechseal and bearings fail, isn't it because of misalignment?
Thanks and Regards,
MW
RE: Bellows after pump discharge
RE: Bellows after pump discharge
I suggest that you check alignment as usual and then position a dial indicator in an appropriate position on the pump bearing housing and put the pump online, any movement on the dial gauge will show you if in fact you have any movement of the pump during operation.
International College
Naresuan University
Phitsanulok
Thailand