VS4 type pump

[Divya11]

When we are buying a VS4 type pump where the discharge pipe is separate and we specify a discharge pressure requirement, does the vendor consider that requirement at end of the discharge pipe flange (top of the baseplate) or at the interface flange between casing and the discharge pipe?

 

[Artisi]

Consult with the vendor, or be specific in what your specification says.

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.)

 

[Divya11]

My process engineer says that the pressure that they have asked for is at the interface between the casing flange and discharge pipe. Their actual requirement at the pump discharge pipe flange on the baseplate is lesser than what they have specified (assuming some losses in the discharge pipe). What I need to know is what is the general practice? Or is it that we always have to specify the location where the specified discharge pressure is required?

 

[LittleInch]

"and we specify a discharge pressure requirement" - so what does that specification or data sheet say?

I think the vast majority will specify the pressure at the outlet discharge flange on the base plate based on your supplied min inlet head and SG of the fluid. but check, don't assume unless the difference is relatively negligible (4m in 400 won't make any difference, but 4 in 20 would)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

You should always specify what discharge pressure you require at the discharge flange of the pump unit. Losses from inlet to outlet is not your concerns and only the pump manufacturer has this information available

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.)

 

[Divya11]

That is what I also believe that the pressure requirement should be specified at our interface with the pump, i.e. flange at the baseplate. However, the pump vendor would select a pump based on the differential head specified by us. For example, if we have specified a TDH of 15m, the pump vendor would plot the operating point on the impeller curve at 15m. This means that the head developed at the casing discharge flange shall be 15m. As a result, the head received at baseplate discharge flange would be lesser (say 12m). If the process engineer has to consider the discharge pipe losses, he would specify TDH of 18m so as to get 15m at the baseplate flange. In that case the pump vendor would plot 18m on the curve, thus changing the operating point. My concern is who has to consider the head required to overcome the length of the discharge pipe? The pump vendor or the process engineer?

 

[LittleInch]

That's why you don't specify a TDH. You specify a pressure or head at the discharge flange based on a certain minimum inlet head (height of fluid above pump inlet). For most pumps like this the inlet can often vary from a max to a min. Min is what the pump vendor will use to get the pump and motor , max is what you need to use to calculate max flow or pressure, especially if the range of values is quite large compared to the outlet head.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Why are you concerned about the head developed at the pump discharge, simply specify the head required at the flange on the baseplate.
You are just complicating a very simple requirement.

Simply spec. -- "Head required at the pump mounting plate flange is to be 15m." simple, uncomplicated and fully understood by everyone.
This means you are responsible for the differential head of - sump level to discharge point including the friction loss in your pipework - the vendor has no control of this so entirely your responsibility.

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.)

 

[Divya11]

I completely agree Artisi and LittleInch. But my process guy has specified a requirement of 15m head whereas his requirement at the pump mounting flange is 12m. It came as a surprise to me as well, as I believe that whatever our requirement is at the battery limit, should be specified. Now I am all confused. I think I will ask Vendor to confirm the value of head delivered at pump mounting flange.

 

[Artisi]

Think you should clarify your process guys comments initially to see why / what etc he is talking about.

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.)