Expansion joint on pump nozzle

[KyrTh]

Hello,

I am going to install a rubber expansion joint on the suction nozzle of a fire fighting pump and I am trying to find the optimum placement.
Should it be nozzle(6”)-expansion joint (6”)- reducer (6”x8”) or nozzle(6”)- reducer (6”x8”)- expansion joint (8”)?

Do you have any suggestions, good engineering considerations or empirical practices for the subject?

Kind Regards

 

[C2it]

What kind of EXJ exactly ?

If you are installing an unrestrained axial unit, the 6" will clearly cause less pressure thrust. Equally it will have lower spring rates than an 8" unit, although that should not be a problem with a rubber EXJ.

 

[KyrTh]

Thank you for the reply.

I am going to use tied rods so to handle the thrust.
As you already mentioned, the results when using 6" or 8" rubber joint are quite similar.

So I am thinking of the optimum placement regarding the flow, alignment etc and without taking into consideration aspects.

 

[LittleInch]

First off, make sure that you really really need this joint. They are a weak point in in any system and for a fire water system I would try and avoid them.

Without seeing the layout it is very difficult to say that any one location is better than any other, but I would be a little wary about attaching such an expansion joint directly to a pump.


My motto: Learn something new every day

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

 

[bimr]

Most likely you should have some type of eccentric reducer.

http://hosesinc.com/pdf/rubber_spool_RE_221.pdf

 

[KyrTh]

Thank you for the tips.

I totally agree that the exp. Joints should be the last option in a piping system, even if the medium is water.
In my case, this is my last option and it was discussed thoroughly with the client.

I am just asking if someone has a theoretical or empirical approach of which configuration I should follow.

Concerning the possible use of an eccentric rubber joint, I don’t have any experience of their performance during operation (flow, lifetime, alignment, vibrations) so I will definitely not going to use it.

 

[pennpiper]

KyrTH,
What do you mean it is your last option?
What is the fluid?
What are the operating conditions (Pressure & Temperature)?
What is your experience with Expansion Joint installations?
Are you aware that an Expansion Joint MUST have an Anchor on both sides to make it work? You are making your pump the Anchor on one side. What is the material of the Pump?

Sometimes its possible to do all the right things and still get bad results

 

[bimr]

What do you mean regarding: " Concerning the possible use of an eccentric rubber joint, I don’t have any experience of their performance during operation (flow, lifetime, alignment, vibrations) so I will definitely not going to use it."

It is industry practice and recommended by all pump experts to use an eccentric reducer on pump suctions, not a concentric reducer as you posted.

The same people that make expansion joints make the eccentric reducer.

http://www.procoproducts.com/rubspool.html

 

[KyrTh]

Hello once again,

Thank you all for your comments and concerns.

Mr Bimr, I never posted that I am going to use a concentric reducer. You can have a look on my previous posts to verify that.
I just mention that I do not want to use rubber reducer expansion joint.
As I matter of fact have you ever used this item? If so, do you have any observations about its operating performance?

So, concerning my initial question, does anyone have an preference or suggestion in placing the expansion joint before or after the reducer?

 

[Artisi]

If I was going to use a rubber expansion joint on any pump which would in fact be against my better judgement in most cases, I would use it before the reducer for 2 reasons, 1) less head loss due to the larger diameter and 2) probably less turbulence at the pump inlet.
Why do you want/ need an expansion joint?

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.)

 

[KyrTh]

So, that means exp-red- nozzle.
We are dealing with a redesign. The owner commented that he prefers 10D of straight run before the suction of a double suction pump, while everything was already constructed. We have warned him about the disadvantages of using expansions, but he prefers to save money.

In my 12 year career it is just a couple of times that I had to use exp joints on metallic pipe. All of these cases were in water systems only, with low pressure and temperature. So you can say that I have limited experience in using them, but a lot of experience in avoiding those flexible troublemakers.

 

[bimr]

"Should it be nozzle(6”)-expansion joint (6”)- reducer (6”x8”) or nozzle(6”)- reducer (6”x8”)- expansion joint (8”)?"

A "reducer (6”x8”)" is a concentric reducer.

 

[TenPenny]

I had an interesting discussion with a guy that I consider an expert on pipe stress analysis, he showed me why using rubber expansion joints on the pump suction line can easily overload the allowable forces on the pump flange, unless you either use one with tie rods (as you mentioned), or make sure the joint is placed where the suction line is 90deg to the pump inlet. The extra area of that convolution can mean that with even relatively low pressure, the force becomes fairly large.

About three months after that discussion, I ran into another case where the piping designer was trying to figure out where he could use an expansion joint and not overload the pump flanges, and I was glad that I had already had that primer and discussion.

 

[bimr]

Piping should be supported and anchored independently of the pump and not hung off the pump. The problem comes when the piping loads are supported by just the pump. The typical pump is not designed to support piping loads.

The straight run into the pump starts after the typical eccentric reducer that is installed on the pump.

http://www.hydrocarbonprocessing.co...nd-straight-runs-of-pipe-at-pump-suction.html

I am not sure why the OP thinks he needs an expansion fitting either.

The OP said this was for a fire pump which presumably would not be operating 24/7. Some of the design issues will not be as critical since the design issues are focused on long term pump reliability.