How to select the Vacuum for priming the centrifugal pump? 1

[Petroleumman]

Recently, I am involved with a sewage pump station, which are centrigugal pump and is applied for transporting the sewage from one pond to other area.

With regard to centrifugal pump, it is well know that,the inlet pipe of centrifugal pump must be primed, in ordet to avoid the air bind and cause that the water can not be drawn from the lower water level than the inlet of pump. As usual, at the view of cost, installation a foot valve at the inlet pipe is a way to keep the water with the inlet pipe for next start-up, and at the same time, a water tank can be put into the pump station to fulfill the inlet pipe and drive the air out of inlet pipe.

However, the Owner of this project requests to add the vacuum pump to draw water and prime the inlet pipe. Can anybody can enlighten me which plan is better and reliable? Foot valve with priming water tank or vacuum pump? and if vacuum pump, how to select it? which standard or code can be referenced?

Thank you very much at advanced.

 

[djack77494]

A vacuum pump would be quite a bit more complex. It would have to produce enough vacuum to "lift" the sewage from its source to the pump, which shouldn't be "high vacuum". It should have a bit extra in order to open the foot valve and overcome friction losses. Personally, I'd go with the priming tank.
Doug

 

[Artisi]

are you pumping raw sewage and what size s the pump unit.

 

[Whyknot]

A lot of the pump manufacturers supply the complete system Gorman Rupp and Godwin supply packages with vacuum primers.

You may also want to look at a Self Priming Pump. These are used alot in packaged lift stations for pumping sewage. The foot value will work however if a solid keeps the valve from seating you will loose your suction leg.

 

[Artisi]

As pointed out by Whyknot, a foot valve is not a recommendation I would ever make due to the potetial problems it could introduce, likewise a priming tank can also be very troublesome with a build-up of solids etc in the tank.
Depending on your pump size and duty I can offer further suggestions later.

 

[Petroleumman]

Thanks very much for your so quickly response. The inlet pipe is 20inch and outlet pipe is 16inch, and the rated flow is about 1000m3/h. If the vacuum pump is determined to be installed, how to select it? which type is suitable? Thanks a lot.

 

[Artisi]

is the pumped product raw or treated sewage?

 

[Petroleumman]

treated sewage, without the big particle.

 

[Artisi]

One more question - is it a single or multi-pump station?

 

[Petroleumman]

3 sets pumps are installed over there. Thank you very much for you response again.

 

[Artisi]

Unfortunately not knowing exactly what your pump configuration is – but assuming 3 horizontal end suction pumps units of some description – not knowing the pump duties and the physical arrangement of the PS and the relationship between inlet and the outlet point is difficult to be too specific with suggestions.

However, as you started out with saying you have options 1) using a priming tank and 2) using a vacuum pump arrangement to prime the pumps.

Priming tanks have 2 configurations – the first is simply a tank with an inlet connected to the inlet pipework with a foot valve attached to of the tank connected to the pump inlet, usually the inlet and outlet are inline giving a straight thru arrangement to the flow. This is not an option I prefer for your duty as the foot valve is prone to being jammed open from material in the pumped liquor. The second is similar but the inlet to the tank is at a level higher than the pump inlet (again no footvalve) so that pump remains full and the pump primed when it is shut down. Again not a good option in my opinion – as the flow into the pump is very disturbed and can cause problems on the pump inlet side, any incoming air can collect in the top of the tank and gradually displace the incoming product and put the pump off-prime - you possibly need a non return valve on the discharge side depending on the discharge pipe arrangement so as not to drain the back from the discharge point.

My preferred option is a vacuum primed unit/s for a number of reasons –
1. they will self prime from dry
2. any air leakage or air coming in with the pumped flow can be removed
3. the pumps can “snore" and reprime if you have fluctuating inflow
4. the vacuum pump only needs to be sized sufficient to prime the pump initially within a reasonable time and to handle any incoming air in the product to ensure the pump remains fully primed.

The disadvantage is there is higher maintenance on the vacuum primed unit – ie lubrication for the vacuum pump and the air / water separation valve arrangement but overall is a better option than priming tanks .

There are a number of companies making vacuum self priming pumps and will usually supply the equipment as a package to fit your units.
Companies I know are
Andrew-Sykes and Godwin pumps in England
Sykes Pumps and Multiflow in Australia
Possibly Gorman Rupp in the USA

 

[JohnNabors]

Also Thompson Pump in the US

John Nabors

Never try to teach a pig to sing. It wastes your time and annoys the pig.

 

[rmw]

I had a client who pumped water to log sprinklers. The pump suction was return water from the log decks which brought a lot of bark and dirt back from the log stacks along with the return water. They had incessant problems with the solid particles causing the foot valves to fail so that they could not prime the pumps.

I put a vacuum priming system on their two pumps and they never had any problems after that. They loved the system. They were one happy client. I wish all my projects had worked out that well.

rmw

 

[Artisi]

rmw - It's the only way to go - I saw my first vacuum self-priming pump in 1969 and been directly involved in probably a few thousands since then in all types of applications, sizes and configurations.