Hello. I have a 3-year old building, geo-thermal. Climate-Master heat pumps; 6" well-water extraction and injection wells; plate heat exchangers; and 25% P.G. load side. The problem is occasionally when the well pump starts up, it slams the source piping. The pump motor is on a Q9 drive for soft start. I have decreased the acceleration time from 2 sec. to 15 sec. The drive maxes at 50HZ. and I have good flow through the plate heat exchangers at that outout. This adjustment seemed to help as the noise isn't quite as noticeable now but is still there. There is a Taco sand separator in line with the well water supply ahead of the HX's. Blew it down yesterday. One observation I noted--there is a 6" Watts 774 double check valve in-line where the well supply enters the building, lower floor. My observation was that it is installed vertical flow down. The install instructions say it can be installed horizontal or vertical flow up. The plate HX's are located on the second floor. I want to say that the 774 checks are holding in the off-cycle as I isolated the well off water from the HX's on the second floor and opened a 2" ball valve on the bottom of the separator--no vacuum. Normally, if you were to open that 2" ball valve, there is one heck of a vacuum. So, am I dealing with an air issue here? Should the 774 be positioned properly? I hate to do the latter and then still have the problem. This is an intermittent problem, btw. Any input would be greatly appreciated. Thanks. Oh and I'm in Iowa. Cheers!