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phc June 2022 www.phcppros.com

purge configuration. You also have the potential to really push air and dirt around and out of your systems. Trust me, a flush cart is a great tool to keep in your arsenal. For systems slightly larger than your typical residential job, a flush cart designed for geothermal systems can be used. These can often be rented from wholesalers. Filling with a flush cart is all well and good, but without a typical automatic fill valve, how do I maintain static fill pressure? Some say you don't need a fill valve on a system that doesn't leak. It is a true statement, and I agree with it to some extent, but there are always those times when you intentionally create a leak. This could be during the blowdown of a strainer or when your air separator is doing its job and letting air out. Both of these cases will cause a loss of volume and pressure in the system that must be made up. System feeders are typically used to maintain static pressure in those systems without a fill valve and potable connection. These devices store a limited amount of fluid and incorporate a pump and pressure-reducing valve. You'll see them (thankfully!) in many glycol systems. They also can be used in systems without glycol. In jurisdictions where connecting your water supply to your boiler requires a testable backflow preventer, a system feeder is a good way to isolate your boiler from your potable. It also means you can pass on the testable backflow preventer and the costly annual inspections.

Cutting the potable cord, defying convention

Some years ago, I was enlightened by my colleague, Bob "Hotrod" Rohr, about a way to make a system feeder using common hydronic components that I thought was spectacular. With some fittings, two gauges, a fill valve and an expansion tank, you could accomplish a system feeder without a pump. Instead, you use the air side of the expansion tank to "pump" in the fluid if makeup water is needed. On these DIY system feeders (Figures 3 and 4), the outlet of the fill valve connects to the system like normal; you need a drain to refill the wet side of your expansion tank. If you go this route, you'll want to make sure that the air side of the tank is set higher than your desired static pressure on the automatic fill valve. Also, make sure you don't exceed the max acceptance volume of the tank with whatever fluid you're putting in there. Pretty awesome for a low-tech system feeder, right? These feeders not only allow you to isolate your system from the potable water supply, but they also can save a lot of grief if you spring a leak. With an endless supply of water behind it, an automatic fill valve can wreak a lot of havoc with a system leak. I've seen it; it's definitely something you want to avoid. System feeders will maintain pressure, but once you've used up the stored fluid, the waterworks are over. This may not bode well for those in the water damage restoration industry, but they really save the day in conjunction with a low-water cut-off. So, when you're trying to finish up at that last circus sideshow on a Friday night, remember there are many ways to get the job done! Fill 'er up! l Cody Mack has nearly 20 years' experience as an installation contractor, service technician, application engineer and, most recently, as training manager for CaleffiNorth America. He's a family man, gear-head, and motorcycle enthusiast with a common-sense approach to hydronics. Cody can be reached at cody.mack@caleffi.com.

Figure 3: DIY system feeder, illustrated Figure 4: DIY system feeder, actual