Alternate Energy Systems' piston operated LPG/air mixing systems are designed around the patented POM valve. This unique mixing valve is used in several different sizes throughout the range of our products.

The systems described here are intended to be used with existing LPG vaporizers, either as replacement for LPG/air mixing systems from other manufacturers, or in the conversion from straight LPG applications to LPG/air systems. They are very simple in design, easy to integrate with existing equipment, and require only AC 115 V 60 Hz or AC 220/240 V 50 Hz, single phase electrical supply for operation. They can be supplied with several options, including automatic specific gravity control; flow controllers for PeakShaving applications; Modem, Ethernet or Wireless, interfaces for remote monitoring and control; etc. 
 

The amazing simplicity of the POM provides the basis for a mixer design that offers the ultimate in reliability, and that can be manufactured of any material compatible with the medium being blended. Virtually maintenance free, simple periodic maintenance is limited to the removal of the POM top cover, removal of the piston, cleaning it with a solvent, wiping out the piston chamber and replacing the piston and top cover.

By using a piston, there are no design pressure or temperature restrictions commonly found with diaphragms, which have high temperature restrictions or may stiffen and crack in cold temperatures.

Once set, the POM will mix any two gasses at a constant ratio. The most common application is the production of a LPG/air mixture (Synthetic Natural Gas; SNG) which is compatible with natural gas, regardless of the downstream demand. Other applications include NatGas/Air or NatGas/Nitrogen blending to create replacement gas for Digester Gas, Landfill Gas, Coke Oven Gas, etc.

The POM system is a "pushthru" system. This means that it is not necessary to reduce the air and gas to zero pressure, before compressing both air and gas to the desired pressure. The POM system utilizes the existing pressure in the LPG to satisfy most commercial, industrial, or utility applications.
 

How it Works
The dominant gas (i.e. LPG) enters the Mixer at Inlet Port "A". Compressed air enters at Inlet Port "B". Both gases exit together at Exit Port "C".

A small connecting tube connects Inlet Port "A" with Chamber "D",  and another tube connects Chamber "E" (through the piston) with Exit Port "C".

During no-flow periods, the piston "F" rests in the closed position. Upon demand for gas, pressure at Exit Port "C" drops slightly and this depression is passed through the piston to Chamber "E". The pressure at Inlet Port "A" (dominant gas) is greater and, since this area connects to Chamber "D", the piston will rise and fall with demand changes or pressure drops at Exit Port "C". Thus, the piston can accurately measure the flow of gases regardless of the downstream demand.

Ratio Adjustment
A segment "G" cut out of the piston matches the edge of the cutouts in port "A-B". The piston is positioned between a sliding, pinned guide and the top of the piston. A knurled knob, attached to the stem of the guide, easily allows adjustment to be made externally by rotating the guide (and with it the piston), to restrict either inlet port, thereby controlling the ratio of gas and air. The piston is designed with a series of grooves called a labyrinth which generates circular "O" rings or vortices which prevents the gases from transferring between the top and bottom chambers and thereby, eliminates the need for a diaphragm or a mechanical seal such as a piston ring.

AccuBlend™
All AES patented Piston Operated Mixers (POM-30 to POM-80) can be equipped with this option. It consists of an electric actuator, mounted on top of the POM valve, and a controller with PID characteristics. The controller receives a 4-20 mA signal from a calorimeter, gravitometer (such as the GraviBlend™-3), or oxygen analyzer, and compares this signal with a pre-set value, representing the correct mixture. If deviations are detected, the actuator changes the rotational position of the piston in the POM valve, thereby effectively correcting the mixture to meet customer requirements.

• No rubber diaphragms to dry out and stiffen.
• A close tolerance guide for the piston is internal, away from air & gas flow.
• Unique air labyrinth piston seal.
• The piston does not touch bore.
• There are no piston rings to seize: the labyrinth acts as a seal.
• There is no external piping. Operating bleeds and parts are integral within the valve, thereby reducing damage possibilities.
• Available fully Automatic Gas Properties Control (Wobbe Index; O2 content; Specific Gravity; Calorific Value) when combined with the AES AccuBlend™ Control System.
• Configurations for use as replacement gas source for Digester Gas, Landfill Gas, Coke Oven Gas, etc.