Drain valve between check valve and gate valve

It is needed when purging pipelines.

Used for venting and filling the pump before starting a new pump, to prevent air locking in the pump. Because with a check valve in place, it is no longer possible to fill the pump by opening the inlet and outlet valves of the pump using a pump. During pump maintenance, the inlet and outlet drain valves can also be opened to drain the material inside the pump.

Back flushing is used for draining liquid; it is necessary to empty the container or check whether there is any material present. Isolation is required when emptying the container to ensure safety during blind plate installation. It can also be used to connect a temporary gas source as a gas supply point during purging operations – it has many uses!

This post was last edited by ylb913 on 2016-3-1 09:26. 1. Not all vent valves are called \"drain\" valves. 2. According to the medium flow direction: a combination of a check valve + vent + valve is indeed quite common. This is not only found at the outlet of centrifugal pumps, nor is it used only with liquid media. 1) As for the venting during pump filling at the pump outlet, placing it in front of the check valve can achieve the same purpose. However, when placed after the check valve, it can simultaneously achieve the function of draining the medium between the check valve and the shut-off valve during pump shutdown for maintenance. To this end, some check valve bodies are equipped with a vent port; only by installing the check valve in a vertical pipe can the liquid be completely drained, otherwise liquid will still remain in the vertical pipe between the check valve and the vent. ——This poses no problem for storage of non-hazardous media; otherwise, check valves should be installed on horizontal pipes. Moreover, toxic media cannot be stored on-site either – other methods such as using tank pumps or shutting down the system for replacement are required. 2) During maintenance, the removal of the material inside the pump relies mainly on the vent at the pump inlet or the plug at the lowest point of the pump head, rather than the vent behind the check valve. 3) At the pressure-charging points of many process pipelines, as well as at the points where gases or liquids are introduced, there are check valves, vent valves, and shut-off valves. The venting mechanism located after these check valves serves to carry out inspections (such as checking the quality of the incoming material or to ensure that no backflow of medium occurs); it is used for venting during forward purging (without closing the shut-off valve), and it also functions to prevent backflow during reverse purging (since the check valve does not allow flow in the reverse direction).

It can also be used for sampling: lol

Sampling in this way cannot yield representative samples of the medium

Sampling is related to flow direction and phase state; it does not always occur from directly below. For details, refer to the relevant sections of SH3012.