by Marc Ward
Clay Times Aug 1999
Last issue I wrote about the need for a valve on every burner, but didn't go into what kind of valve to use....(it's hard enough coming up with new ideas for articles after several years, so I need to stretch out these subjects a bit). There are lots of different kind of valves that folks use on kilns and more kinds that many have never heard of. I'm only going to talk about the valves that should be on burners and the ones that are used but shouldn't. First, the ones that shouldn't be used;
Gate Valves. These are the valves that are most commonly used for in-line water/fluid shutoff. They have a round wheel handle and a "gate" that goes up and down inside the valve body. The valve is non directional (doesn't matter which way stuff is going through the valve). Sometimes you can get away with using these valves, but they are frowned upon by some gas inspectors or totally unacceptable to others. Also the gate can "wobble", causing fluctuations in settings. Best bet; Avoid them.
Globe Valves. These guys look almost identical to gate valves. There is an easy way to tell them apart. The globe valve costs about 6 times as much as gate valves and your garden variety hardware store won't have them. It's very difficult to find one that is AGA (American Gas Association) or UL (Underwiters Laboratories) approved. The advantage they have over gate valves is that they are faster opening and closing, but may not allow the same amount of flow as a gate valve. This is a unidirectional valve (gas must go through the valve in a specific direction indicated by an arrow on the body).
Waste or Stop Valves. Again, from outward appearances, these valves look like gate valves. They have a seal that stops down on an internal opening. NIBCO is a major manufacturer of this type of valve and you may have seen it referred to as a T-22. In most parts of the United States, these valves are acceptable to gas inspectors, but you may have to prove they are stop valves. Remember, they look just like gate valves to the untrained eye. (Sorry to say, but there are gas inspectors that have had zip in the eye training department.) The advantage of these valves is that you can make very fine adjustments with a relatively inexpensive valve. The down side; they are hard to find and may not be accepted by your gas people. This is also a unidirectional valve, so pay attention to the arrow on the body that indicates the direction of gas flow. Use 'em, but check with the powers that be before you get all your plumbing together.
Ball Valves. These valves usually have a long handle, but not always, What they always do though is open and close with a 90 degree (1/4) turn of the handle. Some folks also call ball valves with short handles, gas cocks, but a true gas cock is a plug valve (we'll get to that shortly). Ball valves simply have a ball inside the valve that has a hole through it. Turn the ball so the hole lines up with the pipe and it's on, turn the ball so the hole is perpendicular, and it's off. These are good safe valves that come in AGA and UL flavors. Look for the ones with these initials on the body or handle. A gas inspector will never say a word about them. The only downside is that you may not be able to perform very fine adjustments, especially if you are using high pressure gas. These non directional valves are a standard and pretty bullet-proof.
Butterfly Valves. The ones for use on burners are going to look like ball valves. Instead of a ball though, they have wafer inside that pivots through the middle of the valve. A center hinged flap kind of' thing. These have excellent throttling characteristics (ability to do fine adjustments) and some conform to AGA and UL standards. They cost about twice what a ball valve costs. The other downside is that the ones that are AGA and UL approved are only for low pressure (less than 1/2 PSI). A good non directional valve for household pressure propane or natural gas.
Plug Valves. Many times these valves are simply referred to as gas valves. Though there are bunches of different plug valves, the typical bronze body valve with a lever handle is known as a gas valve. These valves are very similar to ball valves, but instead of a ball inside the valve, these valves have a cylinder that goes all the way through the valve. This cylinder has the same kind of hole as a ball valve and the same kind of 90 degree on/off action. These valves are non directional and inexpensive. The downside is how they seal. While a ball valve has a tightly machined and chrome plated ball that rotates against a Teflon seal, a plug valve generally has a poor metal to metal seal that is helped out with a lubricant. Because plug valves have this goop inside, they are some of the smoothest turning valves there are. They are also are AGA and UL approved. The bad rap on plug valves; These valves aren't designed for constant throttling, but more for on/off service. The lubricant can squeeze out over time or dry out and the valve can become hard to turn or leak. Only use ones that you can easily get to and take apart.
Needle Valves. These kind of valves have a female cone that receives a male cone (the needle). The needle moves up and down inside the concave (female) cone. These unidirectional valves are the some of the most accurate and precise valves made. The problem is finding them that are approved for gas service and then if you find them, affording them. A 3/4 inch needle valve may cost over fifty dollars. Use needle valves for small things like pilots, unless you need fine tuning on the main burners.
Congratulations! you've made it through one of my most boring articles and probably the longest (sorry, Polly...) Hey, valves aren't very sexy and there isn't much one can do to make them so. Maybe just the flickering of burner-fire off their shiny little bodies will help some.