Pump suction line priming 1

[MechP]

Hello everyone,
I’m evaluating cost effective proposals for a flood control pump system that also allows for convenient maintenance. One option is to install dry vertical non-self-priming pumps next to the wet well. The pumps would start with a water level on the wet well above the suction line of the pumps and would stop with a water level beneath the suction line of the pumps.
For priming the suction, I’m wondering if anyone has tried implementing a purge valve downstream of a check valve, allowing the system to purge the air as the water level goes up, but retaining the vacuum during pumping whenever water level is beneath the suction line of the pumps.
I’m attaching a drawing for clarity. Consider that NPSH has been verified. Other elements on the line include a foot valve with strainer and a check valve on the discharge, since another concern is keeping the suction flooded. Any advise or proposals are welcomed.
Thank you.

 

[Heaviside1925]

OP,
I feel an initial statement is counter to your proposed design.

I’m evaluating cost effective proposals for a flood control pump system that also allows for [highlight #FCE94F]convenient maintenance[/highlight]

By your design, you already have two check valves to hold prime, so I would wonder if adding the adding checks and purge valves needlessly adds complexity to the design, on top of reliability and maintenance considerations. Maybe I am missing something, if so, please clarify if you'd like.

 

[MechP]

Hello Heaviside1925
Thank you for your response.
Mainly the convenient maintenance part refers to the pumps. That’s why vertical pumps are proposed, so the can be hoisted wherever on site maintenance cant be done. Also, the proposed arrangement would work as N+1 or one pump on stand-by.

 

[Heaviside1925]

OP,
Let's consider this another way. Vacuum leaks on primed lines are a very common problem and there are plenty of topics here discussing the issue, so one method to reduce the chances of this happening, is minimizing leak points. Consider common leak points being pipe fittings and check valves and rest assured, check valves will eventually leak.
In a configuration without the check and purge valves, you have 5 possible leak points from pipe fittings and 2 check valves inline, so you actually have a little redundancy with the two check valves, but they can still be points of failure.
In your proposed configuration, you have added 3 more leak points from pipe fittings and even though you essentially have 2 additional checks in line, you have added them in an additional leak path.
If your only goal is to assist in initial priming, then all you need is a block valve.

 

[Compositepro]

It would be much more reliable to use a vertical turbine pump in the wet well.

 

[MechP]

Vertical turbine pumps were another option considered, but the owner is reluctant because they have installed these types of pumps in the past with not very satisfactory results. A lot of maintenance issues according to them.
The other option still on the table is submersible pumps. Maybe less amount of possible failure points but at expense of maintenance complications I believe.

 

[Heaviside1925]

OP,
To Compositepro's point. If just given what I think is your application, a vertical turbine would be my first choice. I would discuss the client's past reliability issues and see if they are truly a result of the technology used, or a lack of maintenance or lack of understanding of required maintenance. Submersibles can have their own set of issues. I would also recommend installing the required infrastructure along with the pumps for ease of maintenance such as davits and hoists if not already in place.

 

[Artisi]

Flow, head and frequency of use is a major consideration in the pump selection, is it 10 GPM once a day or 1000GPM for days on end?
There are many solutions to the problem depending on usage.

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.)

 

[LittleInch]

I don't really understand what the issue is here?

ON pump start you have flooded suction. All you need is an air release valve where you place the "purge vacuum valve".

Ditch the foot valve, you don't need it as you have an NRV in the pump suction. Who cares if the suction line empties? When the water level rises above the suction line before the pump starts, any air will be vented out of the air release valve.

But why do you need a vertical pump when the pump is in a dry well?

I also agree with Heaviside that you need to figure out what happened previously as vertical pumps in a well is very common.

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

 

[pierreick]

Hi,
Consider this resource to support your work. You should also consider submersible pump together with vertical pump.
Pierre

 

[MechP]

Ok, thank you all for your advice. I will continue to look into the vertical turbine pumps and submersible options.
As for the initial option for the dry well, the idea of considering vertical pumps is to reduce the horizontal footprint in order to reduce as much as possible the area required for the dry well and also to be able to uncouple the piping to hoist the pump.
Also, I’ve found some manufacturers that can provide purge valves with the option of including a non-return function to maintain the vacuum when the water level is low.