Max back boiler pressure 1.5 bar

[LouiseSJPP]

My back boiler stove states max pressure is 1.5 bar, for a sealed system. Is this going to be the max static (ie, cold) pressure, or the max pressure ever, ie, when hot? If it's the max ever pressure, it's going to be a struggle to keep it this low!

If hot max pressure, I'm thinking to set the cold fill pressure to 0.5 bar. What pressure should I set the expansion vessel bladder to?

 

[muggles]

Is it even approved for connection to a sealed system? The vast majority aren't, and you need all sorts of safety controls if you're going to do it. Get it wrong and you'll be creating a bomb.

 

[LouiseSJPP]

@muggles Uncontrolled heat source, sealed system, bang...

This stove is approved for sealed use. It has a mains-fed cooling coil on an overheat valve (AST in Spanish, not sure in English) and a pressure relief valve on the boiler top. Spanish law prohibits header tanks. I did fit one though, and a gravity circuit to a buffer tank, the CH itself a pumped sealed system onwards from the buffer. The gravity system is not working well, and so I need to pump the primary circuit, and I don't have a lot of head to play with. A sealed system is more legal and with a pressure limiting valve on the filling group, it will have three layers of security.

The biggest risk is actually a hydraulic overpressure, leading to a buckled boiler plate, not an explosion. Expensive and embarrasing rather than dangerous.

 

[Johntheo5]

My back boiler stove states max pressure is 1.5 bar, for a sealed system. Is this going to be the max static (ie, cold) pressure, or the max pressure ever, ie, when hot? If it's the max ever pressure, it's going to be a struggle to keep it this low!

If hot max pressure, I'm thinking to set the cold fill pressure to 0.5 bar. What pressure should I set the expansion vessel bladder to?

If it states 1.5bar then its 1.5bar, period, and the PRV (safety valve) should be set to the same.
If you know/post the EV volume and a roughh idea of the system contents or number of rads then can give exact pressures.

If, for example, assuming EV vol of 12L with a system vol of 85L.
First set the precharge (air end) pressure with the EV disconnected from the system, to 0.5 bar, reconnect the system and fill the system to 1.0bar (cold), the final pressure (on system heat up) will then be 1.36bar.
I wouldn't recommend letting the filling valve opened even if set to 0.5 bar, with the above, you will have a nice water reserve of 3L at 1.0 bar cold so you would have to loose this before the (cold) pressure falls to 0.5bar and warning of possible system leak.

 

[LouiseSJPP]

If it states 1.5bar then its 1.5bar, period, and the PRV (safety valve) should be set to the same.
If you know/post the EV volume and a roughh idea of the system contents or number of rads then can give exact pressures.

If, for example, assuming EV vol of 12L with a system vol of 85L.
First set the precharge (air end) pressure with the EV disconnected from the system, to 0.5 bar, reconnect the system and fill the system to 1.0bar (cold), the final pressure (on system heat up) will then be 1.36bar.
I wouldn't recommend letting the filling valve opened even if set to 0.5 bar, with the above, you will have a nice water reserve of 3L at 1.0 bar cold so you would have to loose this before the (cold) pressure falls to 0.5bar and warning of possible system leak.

Thank you, John, this covers it admirably

Will work out my system volumes and see what comes out.