Flat Plate Heat Exchanger leak?

Alan (California Radiant) Forbes

I've been working on an older solar heating system that keeps losing pressure. Most of the piping is above ground and there are no obvious leaks. I've never seen it, but is it possible for a flat plate heat exchanger to leak to the secondary side of the exchanger with no obvious external signs of leakage, like on the mechanical room floor?

aircooled81

Its possible, put the two loops at different pressures, isolate them from a source that can change the pressure (pumps running, expansion tank, make up water) and throw a guage on both loops. If one is at 20 psig, and the other is at 40psig, you come back in an hour and they both become 30 psig.... Well.
Is there a blow off valve and expansion tank? Could blow off valve be dripping?
Btw, on some buildings i have seen old piping have tiny weeps. These weeps allow so little water to leave it evaporates before it creates a drip. Many of those could cause significant pressure drop.
Dont forget to check the pump seal.

hot_rod

Alan (California Radiant) Forbes said:

I've been working on an older solar heating system that keeps losing pressure. Most of the piping is above ground and there are no obvious leaks. I've never seen it, but is it possible for a flat plate heat exchanger to leak to the secondary side of the exchanger with no obvious external signs of leakage, like on the mechanical room floor?

Does the pressure drop to 0? Gauge pressure will vary widely in a solar as the temperature at the collector will vary widely.

At stagnation condition a flat plate collector can exceed 300°F, At night time, with cold sky re-radiation it can drop below ambient temperature.

If the system has a small fluid capacity and expansion tank you could see 10- 20 psi difference from noon to midnight.

aircool has a good idea to isolate the two circuits, the solar side will still vary over the course of 24 hours.

Alan (California Radiant) Forbes

Thanks guys. The mechanical room floor is concrete, so I would see any active leakage. We just replaced the pump (because it ran dry) and it looks fine.

The secondary side of the HX is a large, 1,000 gallon tank, open to the atmosphere and contains secondary HX's for DHW, radiant and the pool. The pool has been taken offline to have it's own, dedicated solar array.

I want to test the HX by isolating the panels and then pressurizing the primary side of the HX.