Hydraulic Check Valve Types

When I got up to go to the bathroom at 1 a.m. last Monday, my wechat phone rang. It was from Carl, the purchasing manager of Denison hydraulic pump company in the United States. I was very surprised by this phone call. Generally, we communicate with Carl in the form of e-mail and have never used wechat phone. Carl firstly said sorry to disturb my rest, and asked if I could arrange a video conference at 8:00 tomorrow morning. He needs to discuss a troublesome problem with our technical team. I'm concerned that the communication on the phone will not be clear, and asked him to send me a written email first, and then I'll reply to him. Half an hour later, a detailed email with a schematic diagram of the hydraulic system came in. Last week, the hydraulic pump supplied by them encountered problems with his customer. The customer's hydraulic system has been shelved for half a year, and now it needs to be driven. After the operator starts the hydraulic pump, there is no pressure in the hydraulic system. The field engineer judged that there was no flow output of the hydraulic pump, but after inspection, it was found that the rotation direction of the motor was consistent with that of the hydraulic pump, and the oil level, oil temperature and viscosity of the hydraulic pump met the working conditions. The suction system of the hydraulic pump was replaced, including the oil suction pipe and filter. After startup, there was still no flow output. The transmission parts inside the hydraulic pump are intact without falling off, fracture and blade jamming. A week has passed and no reason has been found. Because the hydraulic pump is still in the warranty period, if it cannot be solved in another week, it can only be returned for claim. Carl asked the original supplier of each part for the hydraulic pump and got nothing. After reading the email, I asked him if the hydraulic pump used a hydraulic check valve? Carl said that the hydraulic check valve was provided by HAWE company in the United States, but the after-sales period of the hydraulic check valve has expired. Because AAK supplied hydraulic check valves to their company last year, and the quality was very satisfying, although the hydraulic check valve in this hydraulic pump is not from AAK, he wants to see if AAK technical team can find out the reason. I said there was no problem with the 8:00 video conference tomorrow, because the chief engineer of AAK didn't travel, but I'm not sure if we can help. The next day in the video conference, their engineers showed the whole system. Our chief engineer found that the displacement of the hydraulic pump was 8ml / R, so he asked them to fill the hydraulic pump directly in the oil outlet pipeline, and then start it up. The hydraulic pump still had no flow.