Solar Check Valves

[woodsage]

Take a look at the pix:

Should there be a check valve in the supply line below the 3 way valve and a check valve in the return line above the shutoff valve?

 

[JasonLion]

Typically you have a check valve right after the filter and another one on the solar return line.

Assuming the check valve in the supply line in the picture is after the filter and before any other split offs, your picture looks like a very standard setup.

 

[woodsage]

Is the reason for the two check valves to keep the water in the vertical solar supply/returns line from draining?

 

[JasonLion]

No.

The check valve after the filter prevents water from the panels from draining down through the filter backwards, which could cause debris to get pushed back to the skimmer.

The check valve on the solar return line prevents the panels from being pressurized/filled with water when they are turned off by the diverter valve.

Typically a "leaky" valve is used for the diverter valve so that the solar supply line can drain when the pump is off. The check valve on the return line is setup so draining the line is allowed. It is running water backwards to the panels through the return line that is blocked.

 

[woodsage]

Jason -

Are flapper type check valves the preferred type to use for supply and return?
Is the reason for a "leaky" valve and the draining capability for freezing conditions and off-season?
The flow arrow should be down for the return check valve and up for the supply check valve, correct? The check valves on my system have a flow arrow but they also indicate a direction for horizontal and vertical use.

 

[JasonLion]

Yes, flapper style check valves are preferred. They have the lowest resistance to flow.

You use a "leaky" valve so the panels can fully drain down when not in use. There is presumed to be a separate drain/shutoff for winterizing.

Water should be allowed to flow through the return check valve when coming from the panels and going towards the pool.
Water should be allowed to flow through the supply check valve when coming from the filter and going towards the panels.
Orientation rules may apply depending on the brand/style of valve you are using.

 

[woodsage]

Jason -

Why do the panels need to drain down when not in use?

Should I replace my existing 3 way valve for a "leaky" 3 way valve?

 

[JasonLion]

The panels can get quite hot sitting on the roof when not in use. If they are full of water, i.e. heavy, they will tend to stretch and distort over time, which can shorten their lifetime.

If you bought the valve as part of a solar controller package, it is probably already leaky. If not, you can make it leaky by opening it up and drilling a small hole (1/8 inch or smaller) in the internal panel, connected to the handle/actuator, that blocks the water flow.

 

[pooldv]

Another reason for the drain down is to prevent freezing of water in panels and pushing the hose clamps off. This makes solar start up in the spring much more interesting!

 

[JayBauman]

Another reason for the drain down is to prevent freezing of water in panels and pushing the hose clamps off. This makes solar start up in the spring much more interesting!

Are you speaking from experience, Pooldv?

 

[pooldv]

Nope, I've never had 20' geysers shooting off the roof!