Solar DHW checkvalve issue!!??

[snowcrow]

Installed brand new Caleffi DHW system in November.  The checkvalves only work part of the time and become a real issue when the temperature difference between tank and panel is greatest.  The checkvalves are built into the pump station and can be opened or closed completely.

Is this leakage a inherent problem with this type of checkvalve, or is there a break-in time to deal with?

[dnix71]

All of their online literature mentions keeping the mixer and check valves free of lime scale, sediment and aggressive water. Are you using clean city water or are you on a well?

Their literature suggests adding a sediment filter inline if needed to keep the valves clean.

[snowcrow]

All of their online literature mentions keeping the mixer and check valves free of lime scale, sediment and aggressive water. Are you using clean city water or are you on a well?

Their literature suggests adding a sediment filter inline if needed to keep the valves clean.

I'm talking about solar side, which is a close loop filled with glycel.

[dnix71]

How do you purge air from the closed loop? Any air would mess up the flow. Also the mix has to be right. Car radiators are under pressure with a 2-way check valve (the cap) which has a hose going into an overflow tank. If you don't have the correct antifreeze mix you will vapor lock when it boils. If the hose doesn't stay submerged it will draw back air when the system cools.

Caleffi has a sealed expansion tank instead. But you still can't have air in the closed loop. The position of the check valve in the system makes a big difference, too. My van's thermostat doesn't read or operate correctly if the coolant level gets a certain point low, but the cooling system still functions partially because there are bypass hoses in case the thermostat hangs shut.

[MattM]

Your expansion tank diaphram absorbs the extra volume of coolant as it heats up.  If you don't have a diaphram then you would create a vacuum as the system cools.

[snowcrow]

How do you purge air from the closed loop? Any air would mess up the flow. Also the mix has to be right. Car radiators are under pressure with a 2-way check valve (the cap) which has a hose going into an overflow tank. If you don't have the correct antifreeze mix you will vapor lock when it boils. If the hose doesn't stay submerged it will draw back air when the system cools.

Caleffi has a sealed expansion tank instead. But you still can't have air in the closed loop. The position of the check valve in the system makes a big difference, too. My van's thermostat doesn't read or operate correctly if the coolant level gets a certain point low, but the cooling system still functions partially because there are bypass hoses in case the thermostat hangs shut.

There are two places to purge air from the loop, one air vent at the high side of the collector panels and one at the pump station.  Both the loop and the expansion tank are pressurized to 30psi. (20psi +5psi for each between the pump station and the collectors.)

A radiator cap is not the same kind of animal as the checkvalve I speak of.  A radiator cap acts as a pressure relief valve to allow pressure to escape from the closed loop.  A checkvalve, is an in-line valve that allows the fluid to move in only one direction.  There are two checkvalves in the pump station, one on the hot side (from the collectors), and one on the cold side (to the collectors), to prevent thermal syphoning.  My checkvalves are not closing all the way, thus allowing syphoning to occur, and lose a lot of the collected heat through the panels after sunset

I hope this explains the issue a bit more!

[WindriderNM]

The 2 valves may be fighting each other as the pressure changes and vacuums are created when the system  cools at night.
you might try only 1 valve and see what happens

[dnix71]

Car radiator caps are two way valves. That's why it's important to keep your overflow tank full enough that it doesn't syphon air back into the cooling system when things cool down.

The overflow tank on a car is like your expansion tank. It allows expansion but keeps out air.

A car thermostat inline in the cooling system is supposed to be one way, but isn't completely sealed. For it to sense temperature and open there must be a small flow through it when the engine is running. This is done by means of a small hole in the valve disc. When the temp rises enough it opens fully. For your Callefi valve to work correctly there must be some small bypass. The design of this system sounds deeply flawed.

A sprinkler system with electric control zones has one-way valves that completely seal when not energized. Your system should have been designed with a comparative thermostat that sends an electronic signal to the check valves to open and close at the proper temperatures, otherwise there must be some small bypass through each check valve to allow it to sense temperature properly.

Plus at night when the top side cools down there will be a partial vacuum created and that must be dealt with or it will suck a valve open from the reverse or collapse pipe.

[snowcrow]

The 2 valves may be fighting each other as the pressure changes and vacuums are created when the system  cools at night.
you might try only 1 valve and see what happens

Thanks WindriderNM, but I don't think that's an option.  The two checkvalves isolate the panels, expansion tank, and pressure relief valve from the pump and heat exchanger below them, when the pump is off.  If I open the valve on the hot side, it will make the thermal syphoning worse!  If I open the valve on the cold side, the expansion tank, and relief valve may not fully protect the system. For example, if there is a flash to steam event, with no checkvalve on the cold side, it would allow the glycol to be forced down passed the expansion tank and through the pump in the opposite direction of normal flow.  This could damage the pump over time.

I think you're right about a vacuum forming on the panel side, but I think if I add another 5psi. or so to the system, it may cure the problem   Thanks again for your input WindriderNM

[galeforce jones]

Hi snowcrow,
I just looked at the pumpstation on this link http://www.caleffi.us/en_US/Technical_brochures/01136/01136.pdf
I think this might be the problem, on the single line pump station the shut off and the check valve is built into the same ball valve with temp gauge. In position B when the valve is set at 45° it will not act as a check valve, it must be left in position A for normal operation the valve is now open but acting as a check valve in one direction, you can see this on the link.