Gas Valve

Bill_3

What is the structural difference in a propane and Natural gas valve. One on a hot water boiler.

Unknown

Really no difference except...

in the regulator. Many gas valves today have the regulator built in to the valve (servo regulator). They come usually set up for the equipment they are on LP or Natural. All of the manufacturers of gas valves offer a small kit that can be used to convert the gas valve from one gas to the other. You do however have to be careful as some valves will state on the valve somewhere for Nat only or LP only and can not be converted. In addition to converting the valves you also have to change the burner orifices and the pilot orifice when converting.

Duncan_2

Basic difference.

The basic difference is that propane is a more dense, energy-rich gas, so it takes less volume to get the same heat output as natural gas. Propane uses higher operating pressures with smaller orifice sizes than natural gas. It's a scary thing to see a natural gas appliance hooked up to propane!

For boilers in the 100KBtuh range, I notice propane gas valves will sometimes be slow opening or step opening valves for smooth lightoff, something that's more common in larger burner setups.

Do you see this for natural gas too, Timmie?

Unknown

I especially see

step opening even on low BTU for gas natural gas forced warm air as they have a tendency to roll out on ignition. It depends on the manufacturer being able to get their boiler or furnace through testing as to safe ignition as to whether it is slow opening or step opening.

Very important also it is not a good idea to replace a step opening or slow opening valve with a standard opening.

For those who may not know:

Step opening opens at a lower pressure .7, .9 or even 1.2 inches water column, then 10 seconds later goes up to set outlet pressure usually 3.5" wc for natural 10" wc for LP.
Not to be confused with two stage which is a different set up.

Standard opening opens to full input in 2 to 4 seconds.

Slow opening to full input in 4 seconds or just a little more depending on the valve manufacturer.

Dale

Besides what the other guys said

the propane kit for the valve usually just forces the built in regulator full open. Nat gas is designed to have about 7" in the piping and the valve cuts it to 3.5 inches of pressure. This is because old cities have low 6 inch or so pressure mains in the street and the pressure varies a bit summer to winter cool to cold days. Propane has 11 inches pressure in the house pipe and since it comes from a tank with vaporizing liquid near the house propane just used the 11 inch pressure with no extra pressure reduction at the individual valve. Some valves can't be converted but I can't think of a boiler valve that you can't get a kit for.