How Much Pressure Is Needed on Propane Operated Generators?

Last Updated: August 8, 2022
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Propane is a clean, easy-to-use heat source that can fuel propane grills, home heaters, and even generators for end-users. Generators come in handy during severe weather, hurricanes, and other natural disasters. Commercial electricity is often lost, necessitating the installation of a standby generator.

Propane generators are standard due to the lower environmental risks, increased fuel supply and cost, and ease of maintenance and repair. Have a look at our recommendations for the best propane generator here. Although, from extraction to the storage, propane is put through a series of processes to make it suitable for industrial and residential use.

Why Is Propane Kept Under Pressure?

The answer to propane’s portability is pressure, which allows it to cram so much energy into such a small space. Propane is a flammable gas at room temperature. However, under pressure, the vapor is transformed into a form that is easier to handle and store. Pressurizing propane gas below its boiling point of -44 degrees f (-42 degrees Celsius) at atmospheric pressure produces liquefied petroleum gas or LPG.

Propane molecules are made up of three carbon atoms linked together by eight hydrogen atoms. To preserve the liquid form of propane at room temperature (70°f) and the vapor pressure at 21°c (kpa), it must be held in the tank at a pressure of approximately 850 kpa. You can do this with a strong tank of metal.

At-42°c and below, propane stays in a liquid state, condensing a huge quantity of energy into a small volume of liquid. When the temperature of the propane rises, it starts to “boil” up, and this vapor is a functional source of propane that converts to flame and heats the engines. In this condition, propane gas has a natural response to expand until it is balanced or stabilized by ambient pressure.

Typically, the propane pressure needed to be between 100 to 200 psi for propane operated generators, ensuring that the liquid propane gas stays in a liquid state. > 100 psi are considered low, and <200 psi are considered high. Normally, the pressure inside the propane tank fluctuates somewhat depending on the outside temperature. For example, the regular 70-degree 20 lb propane tank would have an internal pressure of 145 psi. Propane pressure levels above 200 psi are likely to cause the activation of the safety valve typically mounted on the storage tanks. This system allows propane gas to vent or release safely.

The vapor pressure in any size of the propane tank (20 lb, 100 lb, etc.) Will vary on average from 60 to 120 psi. This pressure is not stable and is continuously fluctuating on the basis of the propane temperature and the vapor extraction from the upper vapor region. As the temperature of the liquid propane drops due to the heating, the pressure drops. As the liquid heats up, the pressure increases. Because of this continuous fluctuation, and because engine fuel components operate better at constant input pressures, a regulator must be mounted to maintain the outlet pressure constant or controlled.

In the propane industry, there are two categories of regulators, as mentioned below.

  • Low-pressure. Under this group, there are two distinct types of devices. This regulator can take on several different colors such as green, brown, etc., and is intended to lower the 10 psi pressure to a steady 11 ” water column silver is also a single-stage regulator. It accepts the tank pressure and drops it down to 11″the water column.
  • High-pressure; this regulator, which is usually red in color, decreases uncontrolled tank pressure to a steady outlet pressure of 8 to 12 psi regardless of how much the tank pressure fluctuates.

How to Check the Pressure in Your Propane Tank

  • Use the pressure gauge. This device can be mounted between the shut-off valve and the initial regulator and is especially popular in large residential systems.
  • Release maximum pressure of the tank to the gauge, causing enough gas to flow through to lower the reading of the pressure gauge by 10 psi.
  • Close the shut-off valve and allow the device to stand for three minutes without any pressure up or down. Any rise in pressure indicates a broken valve, while a decrease indicates leakage.

Precautions to Take when Connecting the Propane Tank to The Generator

The worst error regarding propane generators is the incorrect size of the fuel tank. Another critical factor is the vaporization of the tank, that is, how quickly the liquid propane can be withdrawn from the tank for use. Propane fuel suppliers should be able to measure these items accurately, most of which have books and charts that tell us what capacity and scale are needed.

Generator manufacturers will decide how many BTUs per hour a propane generator will require under maximum load.

If a propane tank can’t vaporize the fuel quickly enough, the generator will start to run lean, overheat, and shut down. The vaporizing rate is based on the temperature of the tank that falls as fuel is removed.

As the temperature of the tank decreases, the propane tank will produce frost on the exterior of the tank, even on a hot summer day that compounds the problem.

Most propane fuel systems have two regulators; one high-pressure regulator on the tank, which absorbs variable tank pressure and reduces it to around 10 psi and the vaporizer, which reduces the pressure to a few ounces per square inch and adds air creating propane gas for the generator to burn.

It is vital that the vaporizer is placed above the snow line and that there is a small screen on the air intake; otherwise, the mud wasps will create a nest in the air intake, and the next time the generator needs to work, it won’t operate.

Fuel piping is also an issue since fuel lines should be wide enough to process the BTU. Should the low-pressure lines be too small to accommodate the required BTU, the generator would run lean, causing the same issues of a poorly sized tank.

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I am a mechanical engineer with years of experience working on Internal combustion engine and fixing electrical and mechanical systems, generators, transfer switches, and equipment related to storm water and sewage pumping stations.