Gardner Denver EFD-25 HP Operating And Service Manual Download

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13--8--616

Page 1

SECTION 1
GENERAL INFORMATION

FIGURE 1--1 -- COMPRESSOR CYCLE

COMPRESSOR -- The rotary screw compressor is
a single stage, positive displacement rotary machine
using meshing helical rotors to effect compression.
Both rotors are supported between high capacity roller
bearings located outside the compression chamber.
Single width cylindrical roller bearings are used at the
inlet end of the rotors to carry part of the radial loads.
Ball and roller bearings at the discharge end locate
each rotor axially and carry all thrust loads and the re-
mainder of the radial loads.

COMPRESSION PRINCIPLE (FIGURE 1--1) -- Com-
pression is accomplished by the main and secondary
rotors synchronously meshing in a one--piece cylinder.
The main rotor has four (4) helical lobes 90

apart. The

secondary rotor has five (5) matching helical grooves
72

apart to allow meshing with main rotor lobes.

The air inlet port is located on top of the compressor cyl-
inder near the drive shaft end. The discharge port is
near the bottom at the opposite end of the compressor
cylinder. FIGURE 1--1 is an inverted view to show inlet
and discharge ports. The compression cycle begins as
the rotors unmesh at the inlet port and air is drawn into
the cavity between the main rotor lobes and the sec-
ondary rotor grooves (A). When the rotors pass the in-
let port cutoff, air is trapped in the interlobe cavity and
flows axially with the meshing rotors (B). As meshing
continues, more of the main rotor lobe enters the sec-
ondary rotor grove, normal volume is reduced and
pressure increases.

Oil is injected into the cylinder to remove the heat of
compression and seal internal clearances. Volume re-
duction and pressure increase continues until the air/oil
mixture trapped in the interlobe cavity by the rotors
passes the discharge port and is released to the oil res-
ervoir (C). Each rotor cavity follows the same “fill--com-
press--discharge” cycle in rapid succession to produce
a discharge air flow that is continuous, smooth and
shock free.

AIR FLOW IN THE COMPRESSOR SYSTEM
(FIGURE 4--1, page 13) -- Air enters the air filter and
passes through the inlet unloader valve and on into the
compression chamber where oil is injected into the air.
After compression, the air/oil mixture passes into the oil
reservoir where most of the entrained oil is removed by
velocity change and impingement and drops back into
the reservoir. The air and remaining oil then passes
through the air/oil separator. The air then passes
through the minimum pressure/check valve, the after-
cooler and the moisture separator and into the plant air
lines.

LUBRICATION, COOLING AND SEALING -- Oil is
forced by air pressure from the oil reservoir through the
oil cooler, thermostatic mixing valve, and oil filter and
discharge into the compressor main oil gallery. A por-
tion of the oil is directed through internal passages to
the bearings and shaft oil seal. The balance of the oil
is injected directly into the compression chamber to re-
move heat of compression, seal internal clearances
and lubricate the rotors.