Mash back-flow issue

I brew on a 2 tier stand with the mash-tun elevated above the kettle and HLT. Currently I sparge by turning a pump on/off to regulate the water level in the mash. I also have to close a valve as gravity creates a back-flow back into the HLT. Basically sucking the newly added sparge water back into the HLT. Not a big issue but I'm in the planning phases of a brewery upgrade and one of my goals is to add a float switch that will regulate the mash water level during sparging. So I have to figure out how to handle the back-flow issue.

I was able to find a spring-loaded piston check valve on mcmaster (part #1424T37) made of nylon (w/ 1/2" NPT threads) for about $16. It has a "cracking pressure" of 1 psi. I just don't know how these things work but it sounds like a simple solution. It looks like this:



Any suggestions greatly appreciated.

It's not the easiest solution but you could try making a "Hartford Loop". There was discussion here:

https://www.homebrewtalk.com/f51/my-super-efficient-5-gallon-mash-lauter-tun-92724/index3.html

You could then leave your pump on. Just close the valve on the pump until you get the flow rate you are looking for.