Difficulty priming new pump/filter

[rarara]

My old filter and MPV gave up the ghost, so I replumbed the pool, removing the booster pump that never got used, and upgraded to a glass based 28in filter (rather than the old 31in sand filter that came with the house) with a new 1.5hp astral ctx400 pump

The pool box is mostly below the water level, with the chlorinator setup slightly above water level. The pump is about 1-1.5ft below water level.

My kit is as follows
- Ancient Poolrite S-1800 pool skimmer (i think). I cant find any specs for its port sizes, but they might be a touch smaller than 40mm
- 1.5hp 50mm astral ctx 400
- Zodiac chlorinator
- 28in davey crystal clear glass filter
- 40mm jandy cut offs to the outlets
- 50mm jandy cut off inlet that is supplied by 40mm pipe from the pool-
- 50mm pipe in the box until it gets to the chlorinator

At the moment I have been trying to work out why it wont prime properly. The pump will gravity fill if the lid is removed, and generally starts out with more water but often ends up with somewhere between 25-80% of the basket full, never fully getting to the top and sending a stream of bubbles through the chlorinator and outlets.

What I've done so far;
- Added several inches of pool water & removed the weir
- Ive added a bleed valve to the filter to try and ensure air trapped there hasn't been an issue which hasn't seemed to help much.
- Checked all the unions multiple times as well as connections to the pump
- Removed and replaced pump drain valves (slightly suspect about one possibly having been cross threaded from the factory, but seems to seal on the o-ring with enough pressure)
- Checked pump basket orings etc multiple times
- Wrapped all suction side fittings with plastic to check for suction/air
- Sprayed all suction side fittings with water to check for suction/air
- Tried every setting on the MPV to get prime. Filter seems better than backwash or rinse for whatever reason
- Disconnected the chlorinator, and primed from the highest point in system while valves were off, reconnected then ran from there

Mostly this hasnt improved things much.

I even went as far as running an 800gph bilge pump to push water directly into the skimmer suction port. This seemed to help and got us about as close to primed as I have seen so far, while it was running.

The pool shop guys only suggestion was to keep running it trying to prime it, or to add a non-return valve between the supply cutoff and the pump.

Any suggestions or critique on the plumbing appreciated.

 

[Charlie Bezzina]

Hello. Did you do the plumbing yourself? There are a couple of basic things I would check first, Are all your fittings glued proper? A suction side leak will draw air into the system.
Is there enough water in your pool? Sounds silly I know, but I know from experience.
Is that valve/check valve in the skimmer line fully open/the right way around? Sounds silly again, but it can cause cavitation in your pump which will fill it with air.

 

[rarara]

Hi, thanks for your response.

Yes I did the plumbing, I've done pools before with no issues, however I did check every fitting as best as I could with clingwrap in case I made a mistake on one allowing air in.

I've had the water level up almost to the top of the skimmer inlet to reduce the chance of any issues there

The inlet valve is open and has been tried at several positions. I have wondered if an undersized skimmer suction port with an oversized pump could result in a cavitation situation. Or if perhaps having the pump below the supply line might be an issue.

I've got a plumber coming tomorrow for something else, and I will hopefully get them to pressure test the supply line for me.

 

[Charlie Bezzina]

Incorrect pipe sizes could be a possible reason. The installation manual for my pump states the inlet pipe diameter must be greater than or equal to the outlet pipe diameter, among other things.

Having the pump below the water level should work in your favour actually.

 

[Charlie Bezzina]

Assuming you have a shut off valve on the return side, you can adjust it to compensate according to my pump manual. Also lowering the speed should stop cavitation (if yours is variable speed)

 

[Charlie Bezzina]

Filter seems better than backwash or rinse for whatever

Filter applies some restriction much like closing the return valve. I'd be looking down this path.

 

[rarara]

I've got 2 shutoff valves in the return flow. One outlet was for a pressure cleaner (I think?) and is a much smaller diameter outlet port with a thread in it. The other seemed to be a normal 40mm diameter to two outlet jets.

I've run with each one off with the other on, I guess I could try the old pressure one off and the normal one partly closed easily enough and see what happens. When I ran with just the threaded port open I got some weird bad surging happening so didnt run that way for long.

 

[rarara]

Do you think theres any benefit to adding the non return valve as per the pool shops suggestion?

 

[Bill1974]

Pressure test from the skimmers to the pump. Also see if you can get it to hold a vacuum.

How long does it run before it looses the prime and the basket has air in it? The only way air would get in the basket would be a leak somewhere from the skimmer to the pump or a low water lever in the skimmer and air being sucked in.

What kind of line are between the skimmers and the pump? Rigid or flexible? possible that a flexible line is collapsed and the pump sucks are then?

 

[rarara]

I've also now added thread tape to the pump drain ports, and tried shaving cream on all the suction side fittings in the pool box with no luck.

The plumber (who came for something else) couldnt test it, so now I have to see if a leak detection specialist can work it out on tuesday.

There are rigid lines between skimmer and pump under ground and tiles. It doesnt fully lose prime, but it will go from a full basket (manually primed) to half or quater full fairly quickly.

It did stay about 3/4 full for a few hours today after we had really heavy rain until I turned it off to put teflon tape on the drain ports. After that I couldnt get it to prime as well again as the rain had stopped. Strongly suspecting a crack somewhere upstream of the cutoff valve