Hi, thank you for reaching out to us and for your question :) This does not work with the operating principle of a dosing pump. It can only pump in one direction. But, it can at least partly be solved by using a multifunction valve (MFV) which can provide drainage of the discharge line back into the tank. For emptying the suction side, one has to remove the suction lance from the tank, let the pump run, and again the drain function of the MFV can be used to lead the liquid back to the chemical tank. Be aware that there will still be some remaining chemical in the line. The only way to get rid of this is to flush the pump with water - or any other harmless liquid if water is not suitable as flushing liquid. Hope this will help you! Let me know if you have any other questions! :) Kind regards, Sofie

Our dosing pump rate is between 1.7-3 L/h into a water flow rate of about 4 L/s. Thank you!

The issue here is that the pump identifies that there is not enough pressure difference between the suction side and the discharge side. If there is not enough difference the ball valves cannot close correctly, and the pump will be inaccurate. The reason for that can be very diverse and a lot of them are described in our manual as mentioned. The best would be to make a service with new valves and a new membrane. Check if the counterpressure valve is working fine (minimum 2 bar) and check if the suction line is not too long and no cavitation is there. If all of this is not working, a Grundfos Service Technician should inspect the installation and the pump. If you need more help, please send an email to socialmedia@grundfos.com with installation images and more information on what recommendations you have already tried. You can also contact your local Grundfos service office here: gfos.ly/6051VcpfV. Kind regards, Sabrina.

Hi, thank you for reaching out to us! It seems like there is insufficient backpressure for the pump. You either need to add a pressure loading valve or pressure valve depending on the pump size, flow range used and pump head materials and chemicals. To determine the right valve from our accessories range, I would kindly ask you to provide the following information: - Pump type - Flow rate range used with pump (min. and max. flow used) - And also, what accessories are currently installed around the pump? Maybe you can provide a picture of the current installation. Looking forward to hearing from you and help you further :) Kind regards, Sofie

@@grundfos It's DDA type. Used for Chargepac on marin floc. It's written here 4-20mA, 3.90mA. So, yesterday we replaced the diaphragms, suction and discharge valves. the "low diff pressure" alarm is gone. But then another alarm appears which is "discharge v/v leaks" but there is no leakage outside and my system l shuts down again. Sorry to ask too many questions, i am new to this system. 🙏

Hi again, thank you for providing the above information :) The backpressure seems to be sufficient, so the problem lies elsewhere. There could be several things causing the issue then, but probably the issue is quite simple to fix. May I ask where you bought the pump? I think this requires some guidance on a call and guidance on what to check for. Thanks for your patience! Kind regards, Sofie

@@grundfos i don't know where my company bought this pump. It's a 1 year old cruise ship, quite a brand new ship. So it's built-in everything in the shipyard in Italy.

Hi, ok thanks for the information. Do you then have the possibility to take a picture of the pump, the nameplate and the chemical canister beside it? Thanks so much. Kind regards, Sofie