There are strange issues with the operation of the DEG pipes in our company
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I have a question: Two of the valves for handling materials here keep leaking; I’m not sure if it’s due to the materials themselves. The material is DEG (diethylene glycol). The pump head is 20 M, the speed is 1450 r/min, the flow rate is 6 M3/h, and the power consumption is 2.2 kW. The pump inlet pipe has a diameter of DN50. The pump outlet pipe consists of a DN40 pipe equipped with a DN40 check valve and a DN40 manual ball valve; there is also a DN40 pneumatic ball valve at a height of approximately 8 meters. Between the DN40 check valve and the DN40 manual ball valve, there is a DN25 manual ball valve ； The pump outlet pipe is also equipped with a DN40 pipe and a DN25 pipe that lead back to the DEG storage tank. A orifice plate with a diameter of 10 mm is installed on the DN25 pipe at the point where it enters the DEG storage tank, while there is a manual ball valve on the DN40 pipe before it enters the DEG storage tank, with an opening degree of around 50%. In this case, the pressure during pump feeding is 0.2 MPa; after the pump is stopped, the DN25 manual ball valve located at the DN40 check valve keeps leaking. Leaks continue to occur even after replacing both the DN40 manual ball valve and the DN25 manual ball valve. Is this related to the material being used? Program setting: When feeding material, start the pump first and then the valve (DN40 pneumatic ball valve, with a diameter of DN25) ； When stopping feeding, close the valve first and then the pump. Every time the valve is opened, the DN40 pneumatic ball valve finds it difficult to open; crawling phenomenon also occurs, and fluid shock appears throughout the entire pipeline at the moment of opening. Occasionally, this valve fails to open.
The inlet of this pump is also connected to our discharge pipe; the impact of the inlet pipe on the operation of the pump and the outlet pipe can be disregarded
First, is the material of the D25 ball valve the same as that of the others? Another issue is that your check valve is too tight; after adding material, the thermal expansion of the material between the check valve and the DN40 ball valve causes excessive pressure, leading to leakage at the weak point. It might be better to have that pipe export some material, or simply allow the check valve to leak a little, by adding a small bypass line.
My knowledge is limited, so the following is for reference only: 1. The main cause is usually a problem with the valve. 2. It is recommended to provide the material of the valve, including the materials for the valve body and the valve seat, before further discussion. 3. Provide the pressure rating of the valve. Let’s discuss this together to confirm whether it’s a valve issue.
The last edit to this post was made by cjgj008 on 2018-5-29 at 10:34. My opinion is similar to that in post 3: 1. The influence of the medium can basically be ruled out; diethylene glycol has a high viscosity, making it difficult for it to penetrate, and it also does not cause significant corrosion to valves. 2. If the pump is a centrifugal pump, the relevant influencing factors can generally be ruled out, and its head pressure during operation is not high enough to cause leakage in the valves. 3. I would like to ask whether the pipeline from the pump outlet to the control valve at 8 meters is located outdoors, or passes through any area with high temperatures. My suspicion is as follows: when shutting down the pump, the control valve is closed first and then the pump itself is stopped. The section from in front of the check valve to the pneumatic valve is always filled with fluid at a pressure of 0.2 MPa. If there is sunlight exposure or the external temperature is high, and if the seal of the check valve is particularly good (it’s not clear whether the DN40 valve located behind the check valve is open or closed when the pump is shut down), then the fluid in that section will experience high pressure due to thermal expansion. As a result, it will be very difficult to open the pneumatic valve next time, or the valve may not open at all. Water hammer also occurs when it is turned on; 4. In fact, this situation is very easy to identify: simply install a pressure gauge on the valve located 25 units in front of the check valve, and that will make it clear. 5. Additionally, since it is unclear whether the manual DN40 ball valve is normally open or normally closed, some factors cannot be confirmed. 6. The solution is the same as that on the 3rd floor: add a bypass line or a safety valve to relieve pressure. It is highly recommended to install a pressure gauge on this pipe section to facilitate pressure monitoring. 7. Additionally, it is not clear whether the pipeline from the 40 pneumatic valve to the device section is unobstructed or if there are any valves in that section; the original poster did not provide this information, so it cannot be confirmed. 8. It is likely not related to the quality of the valves; it is mainly caused by unreasonable process design
This post was last edited by lrtlrtlrt on 2018-5-29 at 11:43. Sorry to those who commented above – the information provided was incomplete; I’m now adding the necessary details: 1. Both the DN25 and DN40 manual ball valves are made of CF8 material, with a pressure rating of PN16. The valves are manufactured in Taiwan, and their ball seals consist of white PTFE rings. 2. The pipeline running from the pump to the control valve, over a distance of 8 meters, is located outdoors and lacks insulation; it’s situated in Guangdong. 3. The DN40 valve located after the check valve is normally open. Material was found leaking from the DN25 manual ball valve, so a blind flange has been installed on that valve. 4. A pressure gauge is planned to be installed at the DN25 valve to measure the pressure in that section of the pipeline. 5. The pipeline leading from the DN40 pneumatic valve to the reactor is unobstructed; when the DN40 pneumatic valve is opened, material flows into the reactor. 6. It’s not clear whether a globe valve can be used for this application (after all, globe valves have a hard seal)； I spoke with the company’s chief engineer this morning; it’s not possible to use a globe valve
To determine whether the valve is the cause, one can test the sealability of the valve by checking for leaks at very low pressures; if leaks occur, then the valve is the cause.
Based on the additional information provided by the poster, it seems that the increase in pressure in the section of the pipeline leading to the pneumatic valve is caused by external sunlight and ambient temperature. It appears that the quality of the check valve is quite good, with excellent sealing properties. ;P
Thank you for the guidance :handshake
Haiyou on the 3rd and 5th floors explained it very well!