just replaced Hayward Vari-Flow valve with new inc collar, o ring, Pressure gauge ,,sight glass and sand. I bought the correct sand filter sand (6- 50lb bags). Once the tank was empty I carefully folder up the Umbrella-ish tubes. removed cleaned and inspected them. put it back and put tape over the vertical tube. Filled the tank about 1/2v way with water and re-filled with sand. Removed tape, re-installed multi valve with silicon lubed o-ring and re-connected plumbing. Pump primed aine and began filtering pool. The return jet has a strong flow, the gauge shows 5lbs of pressure. HOWEVER – in back wash water barely flows out of the backwash hose. after cycling through all of the valve positions several times (turning pump off before moving the valve). I took off the top of the valve to inspect and lube the (Spider? O-ring. all looked good so I lubed it and reassembled. Still no backwash flow. I’m stumped. The pump and leaf basket primes fine and all of the air in the cover is replaced with water.
My first question would be is some water returning to the pool on backwash? If you’ve double checked the gaskets, and are sure you have mounted the Vari-Flow valve in the correct orientation that may not be an issue.
Do you have a single speed pump or a variable speed? Depending on the size of the pump and the size of the backwash hose you could be having a restriction.
What size is your filter? When you refilled the filter did the sand only come 3/4 of the way up the body of the tank? A sand filter isn’t full, it’s between 1/2 and 3/4 full to allow enough room for water. Perhaps removing some sand and trying the backwash again would tell you if there was too much sand?
Have you added any filter aids or other chemicals to the pool that would bind in the filter and reduce flow?
If you run a waste cycle vs. backwash is the flow the same or different? If they are the same it’s the pump power that is causing the flow. If the waste is good but backwash is slow then something happening inside the filter is the problem.