Design Information and Specifications

Equipment Selection

To size a gas booster properly the maximum volume (ICFM or ICFH) and the differential pressure ("WC or PSIG) are required. Please note that the ratings of the gas boosters can not be modified without losing the UL Listing. In some instances the required volume is well below the maximum rating of the machine. If this is the case a by-pass line may be needed to recirculate the excess gas. (See Below)


The gas booster system can be designed to run continuously, or can cycle with the demand required by the appliances (if the appliance is so equipped).

All Spencer gas boosters are designed and manufactured to run continuously. Electricity cost, however, may make it prohibitive to run the gas booster when there is no demand for elevated gas pressure.

If a gas booster system is designed to run continuously, care must be taken to note the turn-down or low flow requirements of the appliance. All gas boosters have a minimum flow rating. Depending on the low flow of the appliance and the minimum flow rating of the gas booster, it may be necessary to install a by-pass or reciculation line between the outlet side and inlet side of the gas booster. This by-pass line will allow for a continuous flow of gas through the booster if there is reduced or zero flow required down stream at the appliance. The recirculation can be done manually with a clincher valve that is set during start-up and locked into position or can be controlled using an electronic modulating valve. Depending on the temperature of the gas at the outlet side of the booster, a heat exchanger may be required in the by-pass line to cool the gas before it reenters the booster.

Some appliances are available with contacts that will allow you to start and stop the gas booster on demand. Since all Spencer gas boosters are supplied with three phase induction motors, the motor manufacturers recommend a maximum of three (3) to four (4) starts per hour. It is recommended that a minimum run timer be installed with the motor starter, so that once a booster is started it will run for approximately twenty (20) minutes at a time, thereby reducing the number of starts per hour. Depending on the flow requirements a by-pass line may be required.


The minimum controls that are normally required include a low inlet pressure switch and a motor starter - with provisions to connect thermal overload protection from the motor and the pressure switch. All Spencer gas boosters are equipped with thermal overload protection to prevent the motor from overheating. The leads must be connected in accordance with NEC and local codes. The inlet low pressure switch is designed to disable the gas booster when the inlet gas pressure drops below a specified level, preventing booster from draining the city supply.

Spencer has the capability to design and manufacture specialized control panels to incorporate the above basic controls, by-pass controls and to incorporate any additional functions that are required.

Attached, please find two typical Sequence of Operation sheets illustrating a basic control panel and a basic control panel with modulating by-pass line and minimum run timer.


Spencer recommends that all gas boosters be mounted on a level pad and rest free on cork mounting pads, furnished with each machine. Gas tight flexible connections should be installed to isolate the gas booster from any external stress or vibration from the piping system. A gas tight check valve is commonly required by the local gas utility to prevent any back pressure from entering the supply line.

Please feel free to contact us with any questions on machine selection, controls, or to review your specific application.