The Navy uses three types of air dehydrators for drying LP air. These are the refrigeration (type I), desiccant (type II), and combination of both refrigeration and desiccant (type III). HP air application uses only the type III. The Navy is replacing the various types of desiccant used in the fleet with activated alumina beads in 1/8-inch diameter spheres. This type of desiccant is also intended to reduce dust problems produced by the other various types. The dust causes clogged filters and other component malfunctions.

MAINTENANCE OF LP AND HP AIR DEHYDRATORS

Follow the scheduled maintenance of LP or HP air dehydrators according to the PMS requirements. The following is a sample LP air dehydrator maintenance schedule and is for general information only:

1. Daily:

- Check applicable power on lights, flowmeter readings, cooling water temperatures, heater temperatures, and outlet air temperatures for proper operation.

- Note any dehydrator filter element pressure drops for element replacement.

- Periodically blow down and clean the conden-ser water strainer.

- Blow down type I and type III dehydrators.

Dump the valve if more than 1/2 pint of water drains out; the automatic feature is not working.

- Check the purge pressure and the free move-ment of the purge flowmeter float of type II and type III dehydrators.

2. Weekly:

Blow down the inlet separator, prefilter, and trap dump valve of dehydrators by opening the manual drain valve.

3. Monthly:

- Check the outlet air moisture content. The dew point should be below -40F at 80 lb/in2 for both type II2 and type III dehydrators, and below 40F at 80 lb/in for type I dehydrators. An excessive dew point indicates a malfunction.

- Check the inlet and outlet filters and the purge filter for the type II and type III dehydrators. Replace the filter elements if necessary.

4. Quarterly:

- Clean the condenser water tubes.

- Disassemble and clean the inlet and interstage separators and purge the solenoid valves.

5. Annually:

- Remove and calibrate the pressure gauges. Adjust them to give maximum error 2 lb/in2 (1 percent of full scale).

- Disassemble the desiccant chambers. Clean the assembly of dust, oil, and dirt. Replace the desiccant

Figure 6-5.A maintenance Index page (MIP) for one design and make of high-pressure air compressor systems (page 1 of 2).

if it is significantly powdered, burned, or discolored with oil carry-over.

- Remove the desiccant chamber check valves. Discard and replace them with new items. Adjustment and repair of the dehydrators and their components should be accomplished according to the appropriate equipment technical manuals.