Does a slow-speed recip need to be grouted in? 1

[KernOily]

Hi guys. Looking for opinions here... In your opinion, does a slow-speed recip pump need to be grouted in?

Pump in question is a Gaso 1753 duplex piston pump. Operating speed is about 76 spm, 900 rpm motor, belt drive. The pump and motor are mounted on a pretty beefy structural steel skid. Thanks! Pete

 

[gr2vessels]

Pete,
The grouting is realted to the levelling requirements of that pump and perhaps, filling up the gaps under the baseplate when anchoring the assembly.
It also helps to stabilise the equipment on a flat surface generated by grouting (in association with bolting down).
Then again, if there is no concern with possible movement of the unanchored pump assembly, then the grouting is useless.
cheers,
gr2vessels

 

[BigInch]

Other than the pump itself, it can depend a lot on if 900 rpm is near the natural frequency of the supports.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Typically I don't grout small pumps like yours. BUT I do make sure there is mass under it and that the pump is tied down to the mass.

Good pulsation dampers are a must too.

 

[KernOily]

Thanks guys. Based on your input and on data from other resources, we have decided to place 1-1/2" of epoxy grout under the skid rails only. The original design was to epoxy grout under the rails and fill in the rest of the skid with cementitious grout, as one would do on a large centrifugal pump, but I have decided that would be overkill.

I do not know the natural freq of the pump + baseplate. The foundation is designed with mass > 5x the mass of pump + baseplate and uses embedded anchor bolts. Once the skid is set, bolted down and grouted, I should be OK in the vibration dept. I have pulsation dampeners on both suction and discharge.

Thanks! Pete

 

[electricpete]

How many horsepower?

Some thoughts:

I would think a recip demands more care to the foundation than a pump.

A large foundation accomplishes nothing if the baseplate is not securely attached.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[KernOily]

Thanks electricpete. Motor nameplate hp is 75 hp. As you will read in my last post, the pump skid is anchor-bolted to the foundation.

You are correct - a recip demands more of a foundation. Hence the 5x mass requirement. This is a slow-speed pump, so the requirements are not as rigid as, say, a 450 rpm gas compressor. Thanks!

 

[BigInch]

With that low power, you'll probably be OK. The pump shouldn't be much trouble. Its the motor speed that might be the critical item there, but unbalanced forces within a motor are generally pretty small. 5X mass is usually not too far wrong for that power range and start & short circuit torques. I think normal grout would be OK under the rails too, if done up well, but you can't go wrong with epoxy.

http://virtualpipeline.spaces.msn.com

 

[rcooper]

I had a small progressive cavity pump, about 11kW, running slowly and fitted with a direct on line starter. It was commission and started running before it was grouted in. After a couple of days it had pulled its anchor bolts out of the foundation. It ran every 2 hours for a few minutes and pumped into a 100mm nb pipe around 300m long.

It wasn't the speed of the motor that was the problem. It was the forces generated as the pump very rapidly accelerated the fluid in the pipe up to full speed, and just as quickly (probably quicker) brought that fluid to a hault. As you are looking at a reciprocating pump here, if it is on DOL startup, I would ensure it is grouted in and the grout has gone off before commissioning it. If it is on soft start or VSD, you will probably be okay without the grout.

This force produced during the acceleration of the fluid by a positive displacement pump is large compared with the force generated by a centrifugal pump, which is simply the closed valve head of the pump.

 

[BigInch]

That's worth a star.

http://virtualpipeline.spaces.msn.com

 

[Cheddarcaveman]

If you don't grout, any movement/shock from the pump will be transferred to the pipework and its supports. This could lead to premature failure of piping and supports.
I would certainly recommend that all machinery be properly installed, levelled and grouted as I am sure the manufacturer recommends.

 

[rzrbk]

Unless your foundation is weight limited, filling the skid with cementious grout is cheap insurance against vibration.
Also, an unfilled skid will quickly collect dirt, water, plastic cups, etc.

 

[KernOily]

Thanks. As you will read in my previous post, I said the pump skid will be grouted in under the skid rails and the skid will be properly anchor-bolted to the foundation. We are using epoxy grout, anchor bolt sleeves, tack-welded nuts and washers, taping of anchor bolts in the grout area, squishy stuff in the sleeves under the grout, proper grout curing, etc. We are NOT taking shortcuts here. I also said above that the mass of the foundation is > 5x the mass of machine + base, which is the standard recommendation for reciprocating machines. This ain't my first BBQ ;-)

About the only reason I could see for filling in the entire skid with grout was to keep out trash. The operator has to have something to do...

 

[electricpete]

I certainly have never designed a foundation, just looked at them around our plant. Just interested to understand.

You'll dig two troughs in the top of the foundation just under the skid I-beams will be and fill them back to approx the original level? Or trim off the whole top of the foundation flat(laitence or whatever they call it) and just build two troughs of grout on top?

The second option sounds kind of ugly. The first option sounds like you've got no support on the sides of the grout. Isn't there a poisson's ratio effect going on where the grout is stiffer vertically if it can't expand horizontally?





=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

on my last comment, it's not really the stiffness I was thinking of, but that the grout might crack if it is free to expand horiziontally when compressed vertically

=====================================
Eng-tips forums: The best place on the web for engineering discussions.