Pump pressue fluxuation - with and without solar heating

[Bart]

They finally finished my pool which has solar heating installed. During the indoctrination, the pool company told me about backwashing the filter and adding new DE when ever the gauge on the filter went to the "dirty" setting. Seems easy enough, but I'm a little confused because of the pressure changes when the solar system is being used.

At night or in the early morning, the temperature is not high enough, it the bypasses the solar system. When this happens the pressure at the filter is around 19 psi (the very low end of the "Clean" setting). When the sun comes up and the roof heats up, the solar system kicks in and the water is piped up to the roof and back to the pool. This obviously causes the pressure at the filter to increase. When the solar is working, the pressure is around 26 psi (near the high end of the "Clean" setting and close to breaking into "Dirty" territory).

So my questions are:

1). Should I not backwash the filter until the pressure reaches the "Dirty" limit when the solar system is not running? In other words, only read the pressure with pool-only circulation, not circulation through the solar system?

2). If the gauge reads say 26 psi without the solar system being active (close to the "Dirty" pressure) and it jumps 7 psi to 33 psi when the solar is active (beyond the "Dirty" limit) will the increased pressure hurt the pump or filter or anything else?

Thanks!
Bart

 

[Bama Rambler]

1. You should use the pressure reading without the solar running to determine when to backwash. Don't worry about the pressure jump when the solar kicks in.

2. You won't hurt anything by going into the "red" with the solar running.

 

[lbridges]

+! with the above.

Even if the pipes were free of friction, no problems with flow rate, etc., you must expect the pressure to rise 0.433 PSI for every foot of height difference from the gauge location to the highest point of water flow in the solar system. In other words, it's normal for the pressure to be go up when the solar system is running.

 

[Richard320]

I triple that sentiment!

My pressure varies depending on how I have the valves set. Sometimes as much as 6 psi. You can almost reach the filter from the spa, whereas the furthest wall eyeball has to be more than 40 feet of pipe away. More distance = more resistance = more pressure. Just pick one setting to use for your clean baseline and only worry about pressure change when you're at the same setting.

 

[mas985]

Even if the pipes were free of friction, no problems with flow rate, etc., you must expect the pressure to rise 0.433 PSI for every foot of height difference from the gauge location to the highest point of water flow in the solar system. In other words, it's normal for the pressure to be go up when the solar system is running.

That is only true during the priming phase of the panels. Once both sides of the plumbing are filled with water (i.e. primed), there is static head loss going up the pipe but there is also static head GAIN going down pipe so there ends up being zero net static head change. You still need to take it into account for the vacuum release valve but after priming, static head does not add to total head loss because the water returns to the same elevation from which it was pumped.

The reason that the pressure rises with solar is strictly due to the dynamic head loss in the solar plumbing and panels.

 

[Bart]

Thanks folks!