Fuel Gas Safety Manometer
Posted: Thu Jun 14, 2012 5:25 am
Installed new gas burners into the Margaret S, and wanted a manometer to measure the fuel gas pressure to the burners. Typical gas pressure for aspirating burners is 11 inches Water Column (In WC). The burners here run OK with gas pressures ranging from 2 in WC up to 12 in WC, so I can adjust the burner output according to how much steam is needed to run the engine.
An ordinary “U-Tube” type of manometer could have been used, but the device pictured has safety features that are worthwhile. If the gas pressure is accidentally turned on too high, the manometer water seal will be blown out, and gas will issue from the manometer atmospheric pressure vent. Since Propane is a heavy gas, it would accumulate low in the boat if there are leaks, a safety concern. Therefore the manometer outlet is directed overboard.
If the manometer water is blown out by excessive gas pressure, this manometer automatically resets itself without having to refill the clear manometer tube. There are two water reservoirs, or "Pots", each having a water surface area that is several times the area of the clear indicating tube. Normal gas pressure is connected to the lower Pot, and drives the water column up the clear tube to measure gas pressure. But if there is excessive gas pressure all the water in the lower chamber is blown into the top chamber, then any passing gas is vented overboard. When gas pressure is reduced by the operator, the water in the upper chamber can flow by gravity back down to the lower chamber, and the manometer function is restored without having to refill anything.
An ordinary “U-Tube” type of manometer could have been used, but the device pictured has safety features that are worthwhile. If the gas pressure is accidentally turned on too high, the manometer water seal will be blown out, and gas will issue from the manometer atmospheric pressure vent. Since Propane is a heavy gas, it would accumulate low in the boat if there are leaks, a safety concern. Therefore the manometer outlet is directed overboard.
If the manometer water is blown out by excessive gas pressure, this manometer automatically resets itself without having to refill the clear manometer tube. There are two water reservoirs, or "Pots", each having a water surface area that is several times the area of the clear indicating tube. Normal gas pressure is connected to the lower Pot, and drives the water column up the clear tube to measure gas pressure. But if there is excessive gas pressure all the water in the lower chamber is blown into the top chamber, then any passing gas is vented overboard. When gas pressure is reduced by the operator, the water in the upper chamber can flow by gravity back down to the lower chamber, and the manometer function is restored without having to refill anything.