A hundred years ago, most engines of 6hp or larger – especially oil field engines – were equipped with a gasometer. This was necessary to reduce field gas pressure and provide the volume of gas required by the engine. There are two types of ometers: wet and dry. The dry ometer used a rubber diaphragm. The constant motion eventually caused this to leak. For this reason, dry ometers went out of favor and today are almost nonexistent. Wet ometers are still in use. Some are a hundred years old, as is the one in the photo. The only part needing attention is the stop, which should have the core cleaned and greased once a year.
The bottom can is filled with liquid to approximately 4 inches from the top. Crude oil was used in the oil field. This gasometer is filled with anti-freeze to keep oil off my porch. Note that the gas enters on the left from the field, in this instance, from a propane tank. The small line, teed off, goes to the hot tube of a 15hp engine permanently installed inside the building. The gas goes up, over, and down to a common gas stop, down to the bottom of the ometer, up inside of the can, to the top of the can. Another pipe (not shown) stands upright inside the can, and leads to the right side to the gas hand valve on the engine. In this photo, the gas is off, the top can is down, and the linkage has the stop opened. As the gas is turned on, it enters inside the can, is trapped above the liquid level, and causes the top can to raise and close the stop.
As the engine calls for gas, it is taken from above the liquid causing the top inverted can to drop, thus opening the stop.
A medium point is reached where the gas required for the engine opens the stop enough to let in the amount equal to the demand and the ometer can thus reduce excessive field pressure and provide a constant volume at the same time.
In the oil field, the ometer was located a short distance from the powerhouse and was protected from the weather by a small building that looked a lot like an outhouse. This kept the rain out, which would freeze in cold weather. The ometer shown here had a leaky bottom, typical for ometers this old. I cleaned it well and sealed it with spray truck bed liner. It should last another 100 years or so.