The water is located between two large parallel glass plates of about 15 to 20 mm thick. The glass plates are inserted in the housing by pressure pieces, which are provided with narrow slots. This allows the water level to be visible. In order to prevent chemical attack on the glass, the glass on the water side is protected by a plate of mica.
Behind the glass a lamp is inserted, so that the water level is clearly visible. For pressures greater than 24 bar, steel valves should always be used instead of taps. The houses are made of forged steel, the seats and the valves of Monel metal or nibrometal made. The spindles are of stainless chrome-nickel steel. This is placed on the steam side, and on the water side two steel valves in series. The first is a rapid shut-off valve, the second shut-off valve with a hand wheel in order to render the device inoperative.