Dual Seated Gas Valves (Redundant Valves)

Tim McElwain

This has come up several times recently so I would like to alert everyone to what is code.



Since 1979 all heating gas valves have been required to be dual seated valves or have an ECO back up safety attached to the thermocouple on the valve system.



When replacing an older valve (single seated) it is required to bring the valve up to code and replace it with a dual seated valve.



How do you know if a valve is dual seated?



If it is a Honeywell valve it will have an "R" in the numbering example; VR8300A



If it is a Robertshaw it will have a red handle on the valve, that is an easy one.



If it is White Rodgers most of their valves will be a 36 "E" valve but check the numbers against their catalog.



All of your boilers, furnaces come with a dual seated valve if they are new.



All of your Mod/Con negative pressure valves are dual seated.

Mike Kusiak_2

Diaphragm valve replacement?

Tim, what is required if you have to replace a single diaphragm gas valve on an older residential boiler? Since there is no drop-in dual seated replacement available, do you have to add another diaphragm valve to make the system redundant? 

Tim McElwain

No simply remove

the existing valve and replace it with a new valve from the list in my posting above. If you give me the number of the valve you want to replace I can give you an exact replacement number. I assume this is a residential application as commercial and industrial stuff is different as to application.

Mike Kusiak_2

White-Rodger 26A01-2

The existing valve is a White-Rodgers 26A01 Type 2. This is a plain diaphragm valve without regulator or pilot safety. The regulator is external and the safety is a White-Rodgers bimetal thermostatic switch on the pilot burner. Both crosses for the valve seem to be single seated. Honeywell V8202A1043 or Robertshaw 700-417.

Although this a fairly small residential boiler (178K BTU) the gas train seems more like a larger commercial boiler. I guess this type of setup was common in the 1950's?

Tim McElwain

Mike what we do with those is a complete

retrofit. Remove the regulator, gas valve and pilot. Install a dual seated VR8300A  3/4" x 3/4" Honeywell gas valve Replace the pilot with a thermocouple operated Q314 pilot. upon completion of the install conduct a pilot safety turn-down test to insure safe ignition. The valve will handle up to 250,000 BTU's.



You could also use a Honeywell Y8610U Intermittent Pilot retrofit kit with the Q345 Honeywell Spark Ignition pilot. A redundant gas valve and S8610u Universal module plus wiring harness are included in the retrofit kit.

Mike Kusiak_2

Thanks Tim,

As usual, very useful information.



I am curious about one more situation. What happens if you  have to replace a powerpile gas valve? As far as I know, powerpile valves are single seated. Does the code allow you to replace the valve in this case even though it is not redundant?

Tim McElwain

Yes you can replace

with a powerpile valve and in the case of steam you add a pressuretrol wired into the generator circuit using a terminal block Q313B pilot generator set to open at 14 lbs and reset at 9 lbs just before the pop safety at 15 lbs would relieve.



In the case of FHW an auxiliary limit set at 220 degrees (F) wired the same way with the regular boiler limit at 180 degrees F. You could also use an L8148 L.M or N relay with a built in auxiliary limit.



All functioning much like an ECO energy cut off on a water heater to shut off the millivolts and shut down the system safely in the event of a runaway valve seat in the powerpile valve.

pogg

White-Rodgers 2691-12

I think this old diaphragm valve needs to be replaced. There is gas coming out of the bleed tube continuously while the boiler is firing.

Can you recommend a dual seated valve and pilot assembly to replace it with. It's an old Bastian-Morley boiler (387000 BTU/HR input, 309600 BTU/HR output).

Tim McElwain

That valve is by the way

a bomb waiting to happen. The manual lever allows that valve to be full open with no safeties, actually a runaway gas valve. So it should be removed.



You probably have a bi-metal safety pilot on this system which will have to be replaced with a thermocouple type pilot system with a Hi-Capacity gas valve. It will have to be able to handle 400,000 BTU or higher to meet your application.

This should only be done by a professional who is familiar with proper procedures for doing such a retrofit.

The Steam Whisperer (Formerly Boilerpro)

Converting from 24 V to Powerpile

This post brought the question up in my mind.  Can you legally convert a 24 v newer dual seating system to powerpile using the auxiliary pressuretrol on steam or aquastat on how water?  I really like the Idea of still having heat when the power is out, especially when working with steam.

Tim McElwain

No not legally

however what you do on your own stuff is on you. When the 1979 mandate came down to go to dual seated there was an allowed variance on powerpile which basically added another limit and wired it to kill the millivolts to the gas valve. You could use a pressuretrol on steam set to open at 14 lbs or on FHW a aquastat set to 200 and then your regular limit to 180. Honeywell in fact came out with the L8148 L, M or N which included an internal ECO switch for that purpose. White Rodgers had what they called a "PEPI" switch in their hi-limit only aquastat relay, that one is no longer available

Mike Kusiak_2

Redundant powerpile valves

Tim, what if you used two powerpile valves piped in series, each with its own generator and pilot. One wired normally with the thermostat and working high limit and the second wired separately with a manual reset safety limit at a higher setting. If the main valve were to stick on and cause a runaway condition, the second safety backup valve would cut the gas supply when the safety limit was reached, causing a hard lockout. Since there would effectively be two valve seats in the gas train, would this type of setup satisfy the code requirement?



Seems similar to the two separate gas valves in series used on larger commercial boilers to meet code requirements.

Tim McElwain

No under the present

ANSI Z21 standard it could not be done and I do not ever see them changing the standard as we have moved on into the future of gas heat being Mod/Con and powerpile as a heating system control system is not on any-ones mind anymore. In fact some supply houses do not even carry powerpile valves any more.



As for commercial dual valves they are separate because of Z83 (different ANSI Standard) that along with needing greater internal porting to allow greater cubic foot flow for those higher BTU systems.



On residential valves two in series would create a restriction to flow that would have to be calculated along with perhaps increased pipe size to accommodate that restriction.



I can tell you several valve manufacturers back in the 1980's looked into making a dual valve powerpile valve but soon discovered in the lab that 750 millivolts could not handle two valve coils each of which is around 2 ohms resistance.