Expansion Tank and Check Valve Install

I recently had an expansion tank installed on the cold water side of the HW tank about 2 feet from the inlet. The plumber also installed a check valve just before the tank on the cold water supply line.

The house already has a pressure reducing valve and check valve at the main water supply coming in from the street. The tank installation instructions do not say to install a second check valve.

Will this second check valve at the tank have any impact on the operation of the expansion tank? or the original plumbing?

Will the expansion tank still help to reduce water hammer on the cold water fixtures with this check valve installed?

Thank you,
Andy

As long as the expansion tank is on the heater side of the new check valve, it should work.

Water hammer should really be addressed at the location of the offending valve, although the expansion tank might help a little. Water hammer is caused by quick-acting valves, normally solonoid controlled valves like on a washing machine, ice maker, dishwasher, etc. Some toilet valves can cause it as well. Any place where you quickly turn off the flow of the water. Inertia tries to keep the water column going in the same direction. Stopping it quickly can cause improperly fastened pipes to move, banging into things. Sometimes you get a reflected wave, and that is where the expansion tank might help a little, but it is normally far from the source of the wave. Sioux City and Watts both make hammer arrestors, along with probably other companies. These, when needed, are better long-term solutions. An unprotected air column will get absorbed by the water and prove ineffective after awhile while these with their piston isolated air column won't. A quick and inexpensive version of the Sioux City arrestor for a washing machine runs about $12 or so, less on-line or wholesale.