Hey Carl,
You seem to be blowing the pressure relief valve. So raising the pressure in the expansion tank would only make the problem worse. Did you test your 26psi expansion tank before you pressurized the system? If you did, the 4psi difference (exp tank being lower) is the same way we do it. And if that's what the manual says, then that's not the most likely source of you issues. If not, you can't trust your pressure setting in the tank, just verify it when the system is open (partially drained) so you are testing the precharge with no pressure on the other side of the bladder. But it does seem like you shouldn't be blowing the pressure release either way. Those stainless steel line sets act as little expansion tanks themselves, so you likely have more expansion room than you need. Have you tested to see what the blowout pressure of the pressure release is? Using compressed air or just pushing glycol in with your charging station with the expansion tank isolated? That would be something to verify. Last data point, you had 0psi and then 3" of glycol in the catch container. How much glycol does it take to go from there, to 30psi? if it takes more glycol than you have in the container, than you probably have a leak that you haven't noticed yet. Those stainless steel linesets are very hard to make 100% tight, especially in a steam back system like Schucos. Daniel Young, Lead Systems Designer Dovetail Solar & Wind <http://www.dovetailsolar.com> www.dovetailsolar.com From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Carl Adams Sent: Friday, June 21, 2013 2:18 PM To: RE-wrenches Subject: [RE-wrenches] SHW expansion tank pressure Hello SHW Wrenches, I have a pressurized glycol system which is causing me some grief. The customer called for service after noticing the system pressure was down to 8 psi, and there was some fluid in the glycol catchment container. I inspected for system leaks and found non, recharged the system, and very carefully bled all the air out of the system. Left it run the afternoon and came back next morning to check it. Pressure was down a bit so I recharged it and bled the air several more times. Next day the customer reports the pressure is down to 0 and there is 3 inches of glycol in the catchment vessel. I am beginning to suspect the pressure setting or size of the expansion tank. The system is a Schuco OG300 system, 115 gal tank, Schuco pump station, and 3 CTE 215 collectors (24k BTU/each Clear day C rating). I have a 50 foot SS lineset between the pump station and the collectors with 26 feet of elevation between the expansion tank and the collectors. The expansion tank is a Zimlet 18 liter tank pressurized to 26 PSI. The system pressure is set 30 PSI. These settings are as prescribed in the attached Schuco charging chart. The Schuco pump station shows 1.5 GPM flow when running (WIlo Star 21 pump set at speed 3). In consult with another thermal installer he says he typically sets expansion tank pressure about 5 psi higher than the system pressure. I'd be interested in others practices with regard to system/expansion tank pressure and exp tank size.
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