Re: Blowing down waterglass

I'm assuming that you mean testing the water glass. Here's the proceedure that we use at the Colorado Railroad Museum.
Testing the water glass is a different process than blowing down the water glass. Testing the water glass involves opening and closing the water glass feed lines individually to check for blockages. Also, both valves are checked in the closed position at the same time to insure that they can be completely shut off in the event of a glass failure. This test is performed in the morning while the engine is being prepared for service. It is usually performed by the engineer or hostler, but may be performed by the fireman under the direct supervision of the engineer or hostler.
1. Open the drain valve- the glass should empty and you will hear steam and water blowing out the drain.
2. Close the bottom gauge valve on water feed line – you should notice a change in sound at the drain to more of a hiss and you will see an indication of steam passing down through the glass.
3. Close the top gauge valve on the steam feed line- you should hear nothing at the drain. If you hear or see any emission at the drain, it means one or both of the gauge valves are leaking.
4. Open the bottom gauge valve- you should hear the lower pitched hiss/rumble of water blowing out the drain and you should have a clear glass.
5. Open the top gauge valve- the sound may change slightly as steam is added to the water that is already blowing out the drain. You will see indications of steam passing down through the glass.
6. Close the drain valve – the water should bounce quickly back into the glass and register the correct boiler water level.
7. Open and close the drain valve several times to ensure that the water bounces back to the same level each time.
It is extremely important that both the water and steam valves be in the open position following the test. If one or both valves are left closed, the water glass will not register the correct boiler water level. During the test, the valves should be opened and closed slowly to avoid shocking the glass and possibly causing the glass to fail.