This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
138. Radiator valves, if possible, should all be globe-body compression-angle valves with wood wheel handles. They are usually nickel plated. A brass ground union connection should be made between the valves and the radiators.
139. Valves on steam pipes should all be globe valves, particularly when high-pressure steam is used. The valve stems should always, if possible, be horizontal, or nearly so. This will prevent water from gathering at the back of the valve. Valves on return pipes which are full of water, may be either globe valves or gate valves. The latter usually are preferable.
140. Reducing valves are used for reducing steam from any given pressure to a lower pressure. There are three classes of reducing valves, which are distinguished by their mode of operation: first, those which maintain a uniform low pressure at the outlet, regardless of the fluctuations of the original pressure; second, those which maintain only a constant difference in the pressures at the inlet and outlet; third, those which maintain a constant ratio between the initial and reduced pressures. For all purposes of steam heating, the first mentioned class is the best. They are constructed with balanced valves.