Pressure, flow rate and pool cleaners

Hi, this is my first post :party: Lots of great info on this site :goodjob:

We bought a house about 18mths ago. It had a dodgy pool cleaner (Barracuda I think) that needed replacing not long after and we got a Monarch Systems Turbo Sweep - http://www.poolsmart.com.au/web_images/ ... ochure.pdf

Monarch's website redirects to Davey now so they must have been bought out. Davey's current product looks very similar - http://www.davey.com.au/ApplicationandP ... eaner.aspx

The cleaner occasionally stops moving, like the gears have jammed or there's not enough pressure to drive it. If it is given a light tap/kick, or the pump is stopped/started it will start moving again. Other than that it works really well. We took it back to the pool shop where we bought who couldn't find a problem with it (though all they did was disassemble and reassemble, not test it in a pool).

The pressure gauge on the filter has always read around 50kPa unless a backwash was needed. I recently noticed that the gauge was getting stuck, so while buying a bunch of stuff to get rid of an algae problem I replaced the gauge. Have now found that with the pool cleaner attached pressure reads 25kPa. Without it, pressure is up to 75kPa. So I think the guage that was on the filter before must have been playing up for some time. The manual for the cleaner says it needs 140-200 litres per minute flow rate. The cleaner has ~8m of hose. Does anyone know how to calculate the flow rate based on the pressure difference? It's not possible to measure the length of the pipes going to/from the pump/filter as it goes underground but I can do a rough estimate if it will help. I have the specs for the pump courtesy of the Waterco website.

A pressure drop like that suggests to me that the flow rate is probably not within the specs for the cleaner (and a possible reason for the cleaner occasionally stopping), and maybe I need a bigger pump?
 
Not very often. It was backwashed recently, before I replaced the gauge and got these readings.

I removed a couple of lengths of hose from the cleaner and pressure only drops to 50kPa. Also discovered I had been reading the gauge wrong so the readings were 40kPa with cleaner attached and 60-70 without it. The cleaner hasn't needed a kick yet but I will see how it goes.
 
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