How does this thing work? (Symmons Temptrol cartridge)

[Steve Harris]

When I hooked up my outdoor shower this spring there was no water coming through the valve (a Symmons Temptrol -- appears to be a S242-Body). I removed the unit, took it home and disassembled it. I removed the cartridge (TA-10 "Control Spindle Assy") -- it looks to me like (a) the cold water enters the cartridge from the front, (b) the hot from the back, and (c) the mixed water exits from the center on its way to the diverter/volume-control and then the shower. Twisting the spindle moves the cartridge back and forth, allowing more hot and less cold (or vice-versa) to pass through the cartridge.

The cartridge is a cylinder with a bunch of holes (to allow the water in at the ends and out at the middle), and there is a piston (?) inside the cartridge that slides up and down (back and forth?) when I shake it. I found a DIY video where the guy showed how to free up a stuck piston -- implying that the piston must be free to move and, once freed-up, the old cartridge could be reused.

I assume the piston must have something to do with the "Temperature-Pressure Balancing" function of the Symmons mixing valve, but I don't understand just what it does / how it works. Can anybody enlighten me?

Thanks!

Links:

• https://www.symmons.com/wp-content/uploads/2020/03/S-46-2-BODY_S-46-1-BODY_ZV-3235.pdf
  
• 
  

 

[Jadnashua]

When the water PRESSURE coming in is identical, the sliding piston is centered and lets the water flow freely. If, say, the cold water pressure dropped (someone flushed a toilet for example), that COULD reduce the cold water pressure which would make the outlet of the shower hotter, since there was less cold available. THe sliding valve compensates by decreasing the opposite water supply so the relative BALANCE between the two supplies' pressure stays the same, keeping the water TEMPERATURE fairly even. It's all part of the mandated (since the 80's) anti-scald tech that needs to be in any shower valve assembly. THere's more than one way to do this, but a pressure balance spool valve is the most common.

So, if you only turned on one of the supplies, that would mean zero pressure on the other, the balance spool valve would try to compensate by cutting back the good supply's output, and when new and working well, that will often mean NO volume when only one supply is turned on.

On an older valve, when that happens, it can jam the spool valve to one end and it may not move back once both supplies are restored. Now that it's working, open each valve to the shower control slowly the first time, and equally, and it should be fine.

 

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[Steve Harris]

Thanks!

I did figure out (trial and error) that if I only attach a hose to one of the inputs nothing comes out. But with pressure on both sides the valve works great. In the future, when turning on the water in the spring, I'll increase the pressure, on both sides, gradually.

Thanks esp for the term "spool valve".