Great Lakes Air Products GPS-500 Instruction Manual - Page 7

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DEWPOINT DEMAND CONTROLLER

The Dewpoint Demand Controller is an option designed to limit energy consumption to the minimum

required for optimum dryer performance. The option works off the premise that not all compressed air

conditions are stable and continuous. Each desiccant tower is designed to adsorb the moisture load of

full rated flow and rated conditions for 5 minutes. For example; if at the end of 5 minutes your flow has

fluctuated from 20 to 100% of rated load, the desiccant bed has an unused adsorption capacity of

roughly 40%. At the end of the 5 minutes the demand cycle control holds the freshly regenerated tower

in a pressurized standby mode so the on-line tower can continue to adsorb moisture to the design limit.

While the dryer is in this standby mode no energy is being expended and the overall average energy

consumption is reduced. As the dew point meter (the heart of the Dewpoint Demand Control) signals

that the proper moisture loading of the on-line tower is approaching, the towers invert bringing the

standby tower on-line and beginning the regeneration of the previously saturated tower.

STARTUP

Pressurize the system with the dryer bypass open and the dryer inlet and outlet closed. Then open the

dryer outlet valve allowing it to pressurize the dryer from the outlet.

backwards through the outlet, it allows the control air system to be energized first and properly seat the

control and process valves.

S-L-O-W-L-Y pressurize the rest of the dryer by gradually opening the inlet valve upstream of the dryer.

This will allow compressed air to enter and completely pressurize the dryer. When the tower pressure

gauges indicate line pressure, close the bypass valve and allow compressed air to flow through the

entire dryer package.

Pressurization of the dryer should never be initiated by suddenly pressurizing the dryer towers from the

dryer inlet. The sudden rush of high velocity air in the desiccant bed would cause the desiccant bed to

fluidize. Desiccant fluidization will create desiccant breakdown and or excessive desiccant fines.

This section refers to systems with the optional Dewpoint Demand Systems only

The final step prior to initiation of the dryer is to verify flow to the dewpoint probe in the sample flow

cell. Open the isolation valve upstream of the sample cell filter. The sample cell is now pressurized.

An orifice in the sample cell outlet lets a small flow of air over the probe. After the orifice there is a

check valve that prevents atmospheric air from migrating into the sample cell when the compressed

air system is depressurized. The coil of tubing on the outlet of the sample cell is to prevent

atmospheric moisture from migrating into the sample cell during sampling.

Initiate the "power on" selector switch or push button. Almost immediately one tower will depressurize to

atmospheric pressure through the purge exhaust valve and muffler. At this time verify that the purge

flow indicator (pressure gauge in the purge loop piping) is reading the pressure indicated by the factory

tag located on the piping behind the gauge (the pressure setting for the flow indicator should be

between 45 & 55 PSIG). If the indicator does not match the tag, adjust the globe valve directly above

the indicator until the setting matches. This pressure/flow can be set only during a purge cycle (air

exiting the muffler). The setting will change during repressurization then return to the setting in the next

purge cycle. From this point the system should cycle as outlined in the operation section of this manual.

Once the purge flow is set it will fluctuate slightly during the day if the system operating pressure

fluctuates. It is best to set the purge flow during a time when the system pressure is at a low point, so

the dryer purge requirements are not starved during lower pressure operating periods.

GPS Heatless Regenerative

Page 7 of 14

By pressurizing the dryer