Backflow through pumps 1

[10Gallen]

Hi all,
I am designing a pumped system which will be transferring mildly saline nutrient rich water around an aquaculture project. The animals are very sensitive to H2S at low levels, which is going to form if the water sits in the pipes and goes anoxic. Is there a way of configuring the pump so the column of water can run back through, without having to have manually or otherwise operated bypass valves?
Googling provides a lot of info regarding backflow prevention, and it seems is geared towards preventing the kind of flow I'd like.
cheers,
GAllen

 

[abcmex]

Usually you will allways find a check valve at the discharge of the pump to avoid that the fluid goes back and in some case loosen the impeller.
In Pharma areas they have also problems with stagnant water so they make a small hole on the Check valve to allow a controlled back flow.

RGS

 

[PUMPDESIGNER]

I do not have enough free time to fully consider your situation, but the following may help.

DO NOT allow water to go through the pump without the pump operating, forwards or backwards, bad news (assuming centrifugal pump).

You can inject air into every area of the pipe system including the pump, but in that pump you want to be careful not to lose prime. Small compressor with multiple tubes turns on once in awhile when pump is off.

You can do a combination of drain where easy, inject air in the other places.

No matter which way you go, consider installing atmospheric vacume breakers intermittently and at every high and low spot. This allows your method (drain or air injection) to work properly.

You can install drain valves that close when pressure builds, open when there is no pressure. Install these drain valves in low areas and the pipe in those areas can drain automatically whenever pump turns off. You can get these valves most easily from irrigation supply houses. They are used to drain lateral lines where the lines have large elevation differences, and to drain lines where freezing can be a problem.

Be careful and observant if air is injected. If this is an open system with low pressures (no high pressure or valved off areas), then air is not a big deal unless you have very long lengths of pipe. But in closed systems with higher pressures, valved off areas, or very long lines, air is best considered to be like an explosive capable of destroying things.

PUMPDESIGNER

 

[semo]

As Pumpdesigner stated. Be careful what level you drain your line to. Unless you have a vacuum prime system or self primer, you do not want to lose prime.

I've drained lines in cold climate areas in the following manner.

At a point in the line you are comfortable with, tap the line on the bottom with a smaller line. In that smaller line install a solenoid operated valve. Configure the solenoid as normally open. Wire the solenoid so that it is energized when the pump is energized.

When you do this, the valve will close upon pump startup causing the water to flow through the main line. When the pump is shut off, the valve will open and drain the fluid in the line.

You will also need air/vacuum valves at high points to introduce air. You can size the drain line (solenoid valve) depending on how fast you want the line to drain.

 

[10Gallen]

Thanks for the replies, esp. semo with regard to the solenoid valve, I shall have a closer look.
Regards,
GAllen

 

[dicksewerrat]

I have used a small hole in the check valve on the downstream side of the pump. Then I install a small pipe to this and direct it to the area under the pump. No solenoid. When the pump operates this small water jet stirs the sediments near the pump intake. When the pump is off, this drains the discharge pipe but does not drain the pump. No loss of prime and it does seem to wash new sediments away from the pump intake

 

[semo]

Good thought Dicksewerrat.

I've seen the hole trick done before, just never tried it and I forgot about it. It will do the same thing. As long as the hole isn't too big, the pump won't see a large decrease in efficiency.