Chlorine dosing pump can't pump...

[Davehuge]

Hi all, I'm helping a friend with his 85m3 outdoor pool. We have a problem with the chlorine dosing pump.

Chlorine should be injected by a peristaltic dosing pump but it's not pumping chlorine into the system.

The small rubber pipe from the output of the peristaltic pump is connected to a check valve, the check valve is screwed into a fitting on the 50mm pipe on the return to the pool.

If I unscrew the check valve from the 50mm pipe, the chlorine pumps out no problem proving the check valve isn't jammed or the wrong way round. Once the check valve is screwed back in and the main circulation pump is running, the chlorine isn't pumped out. The peristaltic pump is running but I can see the liquid chlorine and air bubbles in the pipe moving backwards and forwards but not making any progress up the pipe.

1. I believe the pressure inside the 50mm pipe, the water returning to the pool, is too high for the peristaltic pump to overcome and open the check valve. Is this a common problem?

2. As I understand it the check valve is there to protect the peristaltic valve and shouldn't be removed, is that correct?

Just for information, the surface of the pool is at ground level, the pump/filter room is situated below ground level, about 2 metres below the surface of the pool.

[Teapot]

Hi Dave,
What make/model is the peristaltic pump, need to see what pressure it can pump at. With 2 meters of head to overcome + system pressure normally they are easily capable of doing that. That said the dosing point is in the return pipe and is an open circuit so should be absolutely minimal.
Haha the bubbles, they just do that, wobble back and fourth.

I don't have a non return valve on mine or my customers, I rely on the duck bill injector into the pipe work to remain closed unless actually dosing, that is where I think you should start looking, the duck bills degrade with the chemicals and some times they glue themselves together.
When was the pinch tube replaced? That insignificant little tube can cause all sorts of problems except as you state when the check valve is removed.

[Davehuge]

Hi Teapot, thanks for your reply.

The chlorine dosing unit is an Ovy Redox unit made by Melfrance, I'm having trouble finding info about it on the net.

The dosing pump unit is about one year old but has only just been switched on, so you could say it's new.

I was reading the installation manual and it states a maximum pressure of 1.5 BAR is allowed at the injection point / the output of the check valve.

I haven't seen any 'duck bills' on the system so I assume there isn't any fitted.

With the system all connected and running the air bubbles wobble backwards and forwards, when I disconnect the check valve at the injection point I can see it pumps the air bubbles straight out together with the liquid chlorine through the check valve.

Thanks, Dave.

[Davehuge]

Here's some more info...

Chlorine Dosing Unit

Chlorine Dosing 1.jpg (73.82 KiB) Viewed 2082 times

Chlorine Injection Point

Installation Diagram showing maximum allowed pressure of 1.5 Bar

[Davehuge]

I'm hoping to visit sometime over the next couple of days and fit a pressure gauge at the injection point, to see if the pressure there is too high...

At the moment it's the only thing I can think of that could be preventing the chlorine from been pumped in.

[Teapot]

Hmm, 2 metres of head should only account for around 3 psi, what happens if you put your finger over the non return valve? 21 psi should make its way out.

[Davehuge]

Just back from the pool, I was able to use the pressure gauge from the sand filter in the fitting where the chlorine should be injected...

Yes, you were spot on Teapot. With the system running, the pressure is only 4 psi.

I think what's happening is when there's air in the pipe, the pump compressors the air rather than opening the non return/check valve.

So I assume as the pressure is so low, it will be safe to remove the non return/check valve and run the system without it. That should solve the problem and allow the pump to inject the chlorine easily.

Thanks, Dave.

4 psi at Chlorine injection point.

4 psi.jpg (62.82 KiB) Viewed 2040 times

[Teapot]

Hi Dave,
Sorry missed your post, yes i think you maybe right if the bubbles are large enough they will compress. Not had that before as it takes virtually no force to ope a ducks bill type of injector.
You have probably sorted it by now? please let us know how you got on.

[Denniswiseman]

[quote="Davehuge"]Just back from the pool, I was able to use the pressure gauge from the sand filter in the fitting where the chlorine should be injected...

Yes, you were spot on Teapot. With the system running, the pressure is only 4 psi.

I think what's happening is when there's air in the pipe, the pump compressors the air rather than opening the non return/check valve.

So I assume as the pressure is so low, it will be safe to remove the non return/check valve and run the system without it. That should solve the problem and allow the pump to inject the chlorine easily.

Thanks, Dave. [quote]
You could also let the air pump out and then refit the check valve

[Denniswiseman]

You could also let the air pump out and then refit the check valve[/quote]

[Denniswiseman]

You could also let the air pump out and then refit the check valve

[Davehuge]

You have probably sorted it by now? please let us know how you got on.

Yes, it's sorted now. I removed the non return/check valve and I can see the air bubbles are pumped out along with the liquid chlorine. So the dosing unit should take control of the chlorine level now.

You could also let the air pump out and then refit the check valve.

Thanks but I didn't want to do this, I need to make it fool proof. As well as myself, there could be other people looking after the pool. If they replace an empty chlorine tank and air enters the tube, the pump could be running without pumping chlorine into the pool, the chlorine level drops and we end up with a green pool.