Fuel for Thought
Photo #1: Propane feed line branches to the hot tube before reaching the pressure regulator. The hot tube needs higher pressure than the engine.
A frequent question concerning oil field engines is how to connect the gas supply. The majority of oil field engines were configured to run on well-head natural gas. Today, propane is the natural substitution for these engines, but most people have never tried to run an engine on propane until they run into an oil field engine.
In my experience propane -often called 'vapor gas' - is much more user-friendly than one might think. The important thing to remember is fuel and air must be delivered in the correct proportions. How you deliver that mixture to the engine doesn't matter: If the fuel is mixed right, you could just place a hose at the mouth of the engine's intake, and it would run.
Carburetion problems are eliminated with propane-burning engines. Since propane is a gas and needs no vaporizing, all these engines need to operate is a live fuel line. Everyone has an opinion on the best way to plumb these fuel lines, but I'll share what works for me.
In the photo of the 15 HP Reid (Photo #1) the gas supply line enters at the lower left. The propane is plumbed to the hot tube upstream from the regulator, since the hot tube requires higher gas pressure than the engine.
In this case, the hot-tube burner is a Bunsen with a small orifice. A good control valve for this hot tube burner is a hydraulic needle valve, but you can use a needle valve off an old kerosene weed burner. This works very well - maybe even better than an original hot-tube burner valve.
Next, the gas for the engine enters the regulator. I've had good luck with RV-style regulators such as the Marshall Brass #230. Many of these regulator types produce 6 to 8 ounces of pressure but also allow for a high volume of gas. A word of caution, however: Some regulator pressures are too high for an oil field engine. I have found that high-volume, low-pressure regulators work best, as engines can easily flood on propane. Also, check fittings and regulators to make sure they don't have any small orifices (as many do) that will constrict propane flow.
From the regulator, propane enters the engine through a throttle valve. Propane is more combustible than natural or well-head gas, so it doesn't take much to run an engine. I prefer the old dial cock-type valves with a diamond-shaped cut inside for reducing the propane feed to a trickle. These valves are sensitive and need an adjustment now and then. I often give them a slight tap with my pocketknife or the side of a wrench when running the engine. The older-style valves also afford the operator instant control of the gas, from a slight trickle to a large blast. You could use a needle valve with no problem, but you lose that instant control. The proper throttle valve setting is often tricky to perfect on an engine you're unfamiliar with, but trial and error will usually show you the sweet spot on the engine where it starts and runs best.
The old dial cocks can be a problem because many are as old as the engine itself. Also, they're often hard to locate and can be somewhat pricey. Dial-cock valves can be purchased from industrial supply houses and oil field suppliers, but their cost is usually comparable to what you would pay for an original at an antique engine show. If you're like me and have a Bessemer, you'll want to purchase an old Powell valve that has 'Bessemer' stamped on it. Original Reid valves with the large dial and stubby handle are even harder to locate. I still don't have one!
Accumulator tanks are usually placed after the regulator and as close as possible to the throttle valve. I've never needed an accumulator tank on my 22 HP Bessemer or my 15 HP Reid, but I believe that an accumulator can be a big help on larger engines that are hungry for fuel. Many engines won't run on propane without an accumulator tank.
A good rule of thumb is to use an accumulator equal in size to the volume displaced by the engine's cylinder. You're less likely to need an accumulator using a 300-pound propane bottle over a 100-pound bottle.
In the photo of the 22 HP Bessemer (Photo #2), notice the plumbing is routed similar to the Reid, until it passes the regulator. The propane then passes through an original-style driller's wheel bypass, through the governor and then under the engine, ending at the intake valve. With this type of configuration, be certain the driller's wheel valve is closed and the governor valve stays completely open during operation if you want to maintain control at the throttle valve.
Proper regulation and the right throttle setting are essential to operating a propane-burning engine. If the right air-to-fuel ratio isn't achieved, the mixture will not ignite. If you start your engine, and it doesn't fire within a few attempts, shut off the gas and roll the engine over a few more times. This will either cause the engine to fire, or it'll air out the cylinder for another attempt. Never let the gas run too long without this engine running as dangerous amounts of propane can accumulate at the intake and inside the engine.
The best advice is stay safe and always handle propane - or any other flammable materials - with caution. Also, make sure all fittings are good and that all hoses are rated for the pressures they will hold.
As always, please call, write or e-mail if you would like a free membership in the Oil Field Engine Society (OFES).
Contact the Oil Field Engine Society at: 1231 Banta's Creek Road, Eaton, OH 45320-9701, online at: www.oilfieldengine.com or e-mail at: firstname.lastname@example.org