VMAC UNDERHOOD Air Compressor Frequently Asked Questions

The UNDERHOOD rotary screw air compressor has 5 main components. The first main component is the rotary screw air compressor with inlet control valve. This small compact air compressor has two rotors, when the electric clutch is engaged the rotary screw starts to turn. The inlet control valve opens up to allow air and oil to mix between the rotors. The oil makes a seal against the inner walls of the compressor. The more air needed, the more oil flows into the throat to make a continuous seal causing compression of the air.

The engine on the truck will increase in RPM to approximately 2,000 rpm, this will last for 3-6 seconds. When the transducer senses that the tank is fully charged the transducer sends a signal to the throttle control to start to idle down to 900-1,000 rpms. The truck will sit at this rpm until there is a demand for air in the system.

Some of the features are:

• Easy to fill oil plug located on the top.
• Easily removable air filter.
• The air filter is a 5 micron paper element filter.
• The pressure can be adjusted from 100 - 175 PSI.

The RPM is controlled by the Throttle Control. The electronic throttle control works with the transducer. This easy to install throttle follows the pressure drops in the air/oil separator tank. The Throttle Control automatically adjusts by increasing or decreasing the rpm of the vehicles engine to match the pressure drop. The throttle is a closed loop system so it is watching an rpm signal from the vehicle. By watching this signal this will insure that the engine doesn't over rev. The Throttle Control rpm can be adjusted easily by turn the adjustment screw. There is low idle adjustment or idle down pressure screw. The settings you want to have are 900-1,000 rpm on the low idle and 1,800- 2,000 rpm on the high idle. On non-electric foot pedal applications, the RPM controlled by a pneumatic throttle control, which works when there is a drop of pressure in the system. A piston in the throttle is then moved by a spring-loaded piston to move the cable in or out which in turns adjust the RPM of the engine.

NO. The UNDERHOOD Air Compressor System adjusts to the demand of the tool you are using. For an example if you were to run a 35 CFM tool the rpm on the vehicle would be around 1,100-1,300 rpm, once you take your finger off the trigger, the system would idle down to the preset setting of the idle down pressure adjustment. If you were to change the tool to a larger CFM requirement, the rpm would increase to match that the CFM demand of that tool.

The air/oil separator tank is a three-function tank:

• 1st it is an air receiver tank
• 2nd it is an oil reservoir tank, because the UNDERHOOD Air Compressor is a flooded screw; oil is required to be stored for maximum use.
• 3rd this is where the separation of air and oil take place. Oil and air pass through baffles which knocks out a majority of the oil, the air then passes through the coalescing filter, which eliminates the rest of the oil before it is discharged out of the tank. If oil passes through the coalescing filter the oil will drop to the bottom of the tank where the scavenging system picks up the oil and sends it back to the compressor.

The Tank is made out of aluminum. Every tank that is manufactured is pressure tested to 350 PSI for 20 minutes.

Other features are:

• Easily assessable spin on oil filter
• Sight glass to check oil level
• 200 psi safety relief valve
• Rapid blow down cap
• Aluminum spring-loaded sight glass cover.

A liquid-to-liquid cooler cools the system. The cooler is located below the radiator, so there is no interference with the airflow to the engine. The vehicles hood must remain in the closed position when the system is operation so it allows maximum airflow. The coolant of the vehicle cools the heat exchanger. The cooling of the oil is self-contained so it is independent of the engine oil system.

There is a control box located in the cab of the vehicle. The control box has an on/off switch. When the control box is turned on an hour meter will light up, this meter only counts time when the air system is in operation. The control box also has an over temp light. The system will shut down automatically if the over temp light comes on.

There are five safety features:

• The first has already been mentioned which is the over temp sensor.
• The second is the PARKING BRAKE has to be fully applied.
• The third is the drive disable circuit; the DDC prevents the operator from starting the VR70 up in gear. The vehicle must be in park or in neutral before the system will turn on.
• The fourth is the 200-psi relief valve. If pressure should build up in the tank that exceeds 199 psi the relief valve will release so the tank cannot over pressurize.
• The fifth is the automatic blow down cap feature which will drain the tank of air once the system is shut down.