I have a Viron P320 VS pump and Viron EQ SWG on a small 18000 litre pool. A year ago I redid the suction line from 40mm to 50mm (rest is all 40mm) and installed a Flow Vis check valve (measures flow also) on the discharge line going into 25 inch sand filter (in 50mm pipe).
I used the flow Vis to ascertain at what minimum flow I needed to clear the salt cell of gas build up (a known issue with Viron pump when trying to run on low) as manufacturer states min 120 lpm required. I have set the pump on medium speed and tuned the rpm to 2100 (increase of 300 rpm from default) and the flow vis reads roughly 120 lpm for 50mm pipe scale and the cell does indeed stay clear of gas build up so all good.
I was thumbing through my pool equipment manuals the other day and found a pump curve graph for the different default speeds of the Viron. On the chart it states that low should do 121 lpm, med 212 and hi 252 (my sand filter booklet states that 176 is min backwash flow required).
I know that piping size, bends, distance, layout...etc... will all affect the resistance that the pump must push the water through but it seems I am way off the mark from what the vendor states to what the equipment is capable of in my system. I am now concerned that the backwashing may be ineffective as at priming rpm the pump only achieves 160 lpm according to the Flow Vis.
I guess this leaves me with the following paths:
1. I have a problem with my system (piping,pumping, filtering)
2. The vendors specs are fanciful Baloney Sandwich and this is all this pump can do in real life
3. Vendors specs are correct but there is no problem as you really can lose this much flow