A problem with the backflow valve

1. It is a drain valve. 2. It is commonly installed between the front hand valve and the control valve; those I have seen installed after the control valve are basically due to construction errors. 3. In 1994, I heard from the designers that this is called a “incoming material inspection valve”. 4. I understand that control valves usually have low inlet and high outlet, and are installed in front of the valve; this yields a better effect in terms of complete drainage.

Drain valves: In chemical pipelines, the levels of different sections are certainly not the same. Therefore, in the design, a valve is installed at the lowest point of the pipeline or equipment; there are various types of such valves, and their purpose is to drain any residual liquid from within the pipeline or equipment. Corresponding to this are vent valves, which are placed at the highest point of the pipeline or equipment to remove any gas present there. The drain valve is sometimes called a drain valve, and at other times a condensate discharge valve; it is generally a gate valve or a ball valve. Guiding drainage serves basically two purposes: one is for discharge, such as discharging liquid at lower levels, venting gas at higher levels, and venting at the end of pipelines ； The second is used for interfaces of temporary pipelines, such as connecting the system to N2, air, steam, process water, etc. Under normal circumstances, gate valves do not require throttling, which is why they are widely used; although check valves are also used in some cases. A drain valve is a valve used for draining fluid, and such valves are generally installed at the inlet of pumps.

As far as I remember, there are only two scenarios: it can be installed in front of the control valve, or it can be installed on both the front and back sides, as in the case of HF pipelines. The key factor is still the properties of the material.

They are usually installed in front of the control valve to facilitate emptying for maintenance.

You’re absolutely right; that’s not the answer I wanted to hear

There are two options: 1. Install drain pipes between the upstream and downstream shut-off valves, which is a more conservative approach. 2. Pre-installed guide drains, on the condition that the incoming material also passes through the guide drains first. I think it’s because of the pressure from the incoming material, which is reduced after passing through the control valve; that’s why the pre-drain solution is used. If you think it makes sense, please vote for the best response :)

This post was last edited by ljy3033 on 2016-5-27 at 15:13. Some backflow valves are installed between the control valve and the front shut-off valve, while others are installed between the rear shut-off valve and the control valve. What determines this design? Except for hydrofluoric acid or hydrocarbon pipelines containing hydrofluoric acid, the drain valve must be installed between the rear stop valve and the control valve (to remove rust such as iron fluoride); for other media, it is advisable to install it between the control valve and the front stop valve. What is commonly seen on site is that it is installed between the control valve and the front shut-off valve, which is the case in most situations. Since the medium in the pipeline is transported by pressure, if the control valve is closed, the medium ahead of it must be discharged through the drain valve located in front of it; meanwhile, the material behind the control valve has already been transported to a lower pressure area due to the pressure.

The drain valve is primarily used to drain the liquid or gas inside the pipe, and it is correct to install a drain between the two valves~~

8th floor, is there any authoritative source for your opinion, such as standards, manuals, laws, regulations, etc.? Thank you:handshake

A control valve assembly typically consists of a control valve, front and rear shut-off valves, as well as a bypass valve; it also includes the backflow valve mentioned by the original poster. In my opinion, the function of this backflow valve is to drain the material between the front and rear shut-off valves during maintenance of the control valve (usually at times when the material is circulated through the bypass valve of the control valve), and it serves to relieve pressure as well. It is not meant to drain the remaining material in the upstream container equipment, as some people have suggested (usually, there is a separate drainage process for the material at the bottom of the container, involving a drainage valve)