The drain valve must be selected by multiplying the water consumption of the drain valve by 3 times of the water consumption per hour. In order to ensure that the steam trap can discharge condensate as soon as possible during start-up, and the temperature of heating equipment can be increased rapidly. If the energy discharged from the steam trap is not enough, the condensate can not be discharged in time and the thermal efficiency of the heating equipment will be reduced. (when the steam heating equipment starts to supply steam, the equipment is cold and full of air inside. The steam trap is required to quickly exhaust the air, and then a large amount of low-temperature condensate water is discharged to make the equipment gradually warm up, and then the equipment enters the normal working state. Due to the large amount of air, low temperature condensate and low inlet pressure during start-up, the drain valve is overloaded. At this time, the drain valve is required to discharge more than normal operation. Therefore, the drain valve is selected according to the ratio of 2-3. )

2. Working pressure difference of steam trap: when selecting the steam trap, it is not allowed to select the steam trap according to the nominal pressure, because the nominal pressure can only indicate the pressure level of the drain valve body shell, and there is a big difference between the nominal pressure and the working pressure of the drain valve. Therefore, according to the working pressure difference to select the drainage valve. The working pressure difference refers to the difference between the working pressure in front of the steam trap minus the back pressure at the outlet of the steam trap. The back pressure calculation method behind the trap is as follows: (when the condensate behind the trap is discharged into the atmosphere, the outlet back pressure of the trap is zero. If the condensate water discharged from the steam trap is recycled in a centralized way, the outlet back pressure of the drain valve is the sum of the resistance of the return pipe, the lifting height of the return pipe and the pressure in the secondary evaporator (return water tank). )

3. Seat number of mechanical type steam trap: according to different working pressure difference section, mechanical type steam trap is divided into "valve seat number" with various valve seat diameter. Each working pressure difference section and "valve seat number" form a coordinate curve of displacement, and the drainage amount of different "valve seat number" is very different. The appropriate "valve seat number" should be selected according to the corresponding coordinate curve of ≤ working pressure difference and * large displacement under process conditions. The "valve seat number" cannot be determined according to the nominal pressure. If the "valve seat number" is selected incorrectly, the steam trap may not work or the equipment will store water, which will affect the normal operation of the equipment.

4. Working temperature of steam trap: when selecting the steam trap, the steam trap which can meet the requirements of process conditions should be selected according to the steam ≤ temperature of the pipeline. Superheated steam is called superheated steam when the temperature of pipeline steam is less than or equal to the saturated steam temperature corresponding to the nominal pressure.

5. Connection size of steam trap: after the process conditions of the steam trap are determined, the specification and size of the steam trap shall be selected according to the working pressure difference before and after the drain valve, the drainage amount and "valve seat number", and the technical parameters of the drain valve manufacturer. (it is not possible to select and match the same size of steam trap randomly according to the connection size of the equipment. The connection diameter of the drain valve can not represent the size of the drainage capacity. The drainage capacity of the same diameter of the drain valve may vary greatly. Therefore, the selection of the drain valve must be based on the process conditions of the equipment and the parameters provided by the drain valve manufacturer. )