Centifugal Pump Opinions

Choosing between them feels like choosing between your son and daughter, they have different functions but you love them both.

It has been a long time since having the opportunity to choose and I expect a lot of new models and features were added.

End suction with back pull out was nice but split casing also offered nice features. The experience with split casing pumps were that you could specify your duty point and the required efficiency, NPSH etc and it was met.

The efficiency at the duty point would be my first consideration where both is available and unless the circumstance dictates the use of one you will have to motivate the decision to use more energy.

Conclusion : I abstain from voting.

Just the type of biased opinionated comment I expected from you, Hendrik.

Now, does anyone out there have a real bias?

Which is easier to maintain?

Which is easier to install and adjust?

All opinions will not be confidential, and will be subject to public critism whether deserved or not. Later, I will submit my biases, but I am curious what others think.

I have been a pump man for 20 years. I have no bias either way. Split case pumps are typically selected in applications requiring relatively high flows with corresponding limited floor space and ceiling heights. You have to seal a split case pump on two sides instead of one. However, they are typically much more efficient across the range than end suction, resulting in less horsepower. As a rule, I only use them in the cleanest water applications, due to the seal issue. ITT Goulds has just introduced a new model, of which my company represents in Michigan, that looks like it has gained some ground in the mechanical seal chamber area. On the surface it looks like a potential design leap, but I need to see it run at least a year in the field before buying in.

End suction pumps are available the world over. Split case pumps not so much. End suction designs have remained about the same for over 50 years. Split case pumps require a little more technology to get it right.

In what application are you proposing to use one of the designs? I would be happy to comment on the specifics.

Joe T.

Current application, the owner has two pump systems for jet fuel. One system is end suction, the other is horizontal split-case. He wants to have both systems replaced with a single pump system. Right now, my thought is the operating point will be around 700-800 gpm at a 250 foot head.

Fluid is well filtered jet fuel, SG of 0.8, 80degrees F. However, I consider the opinions offered as suitable for other water applications I get involved with. My personal bias has been to the horizontal split case, but part of the rational was the biases of my first boss who was an old time merchant marine engineer. I am curious what current thinking is, to see if I need to adjust my opinion.

Joet@greatlakespump.com

Obviously when dealing with volatile fluids there are several variables one needs to consider. We have extensive experience applying many different pump styles on this type of application. Contact me directly via email and I'll see what I can do to help.

Split case would be the best bet for this application simple to maintain and longer life. Would have a bigger initial cost. This would be offset by lower operating costs. There are a lot of pump companies around who can assist you in this. ITT fluid technology Goulds; Weir Pumps; etc

End suction diffusor type pumps (european) are as efficient as double suction split case pumps. If you have a flooded suction condition use the end suction type. If the suction side needs some special design advantage use the split case. There is not enough information in the question to recomend submerged centrifugals or verticle turbines. Given the choices you gave and not knowing the task requirements leaves me with only one clear choice which is the double suction system.

h2om@hotmail.com

end suction will be much more economical to install and service.The horizontal split case will out last it ten times. IMHO

It depends entirely on the parameters of flow rate,total head,suction conditions etc.

confirm these to narrow down the search.Centrifugal pumps is a vast field !

Cowlagi

Hello Ried,

You never posted your opinions.

Essentially, from what little knowlege I have of pumps, it depends on what you are looking for in the pump. Most end users are looking for the Best Efficiency Point (BEP) for the duty conditions. However, some are just looking for the cheapest initial pump cost not realizing that in the long run efficiency beats initial cost when you look at price savings of the electricity consumed to run it.

Split case pumps generally are easier to work on especially on larger pumps, however in your application you are probably looking at about a 3 inch discharge....relatively small and easy to work on in either instance. When they start getting to about 6 inch and larger, the split case is easier to work on because of the way they open up from the top and the pumps general symmetry. In a large end sucker (usually with a horizontal shaft) the components are too heavy to be manhandled and the loads are almost never balanced.

From a longevity standpoint, generally speaking, Split case pumps last longer (about 4 times) and are more reliable due to more symmetrical loading. An end sucker will usually have a thrust load whereas the split case has none to little. Even if the impeller is hydraulically balanced, when the wear ring wears the hydraulic balance is negated . Also an end sucker will always have an overhung load even if it has a double volute whereas the split case is supported by two equidistand bearings. All these loads help to wear out the seal and bearings.

If suction lift is a problem, I think the end sucker will win almost every time.

More than anything it comes down to a personal preference.

Most pump gurus consider the split case the Cadillac and the end sucker to be the Chevrolet.

I am curious to hear your opinions.

The Captain

Cap'n,

See my post #5. At one point, I worked with an ex-merchant mariner, who was highly opinionated towards horizontal split-case and thus my opinion has always been influenced in their favor. It appears that the consensus of responders to this unscientific poll agree.

Thanks to all responders for agreeing with my biases!

Ried

Must have slept through this thread, hence late response. I agree with most all that has been written already, but cannot resist adding my two cents worth.

I do not have a bias, but have definite preferences based on specific needs.

For your duty roughly translated to metric units of 180 m3/hr and 76 m differential head, and assuming piping configuration was not a constraint, I would go for the end suction back pullout design. The reason being that the slenderness ratio of the shaft for this sized pump would not warrant the extra costs of a horizontal between bearings pump and two seals. Seal leakage accounts for nearly 70% of pump outages so why introduce another one if it is not required.

Well designed pumps of this type in this sort of duty are seeing an MTBM of somewhere between 4 and six years these days.

For very high flow pumps with heavy impellers I would go for the between bearing horizontally split design.

Beware of old marine engineers, not only are we opinionated, but when I was at sea the pumps still had packed glands.