HD372 Compressor
This presentation is a simplified description
of the disassembly of a Blackmer HD372A.
The current production model is the
HD372C (March 1997). Significant changes
are needle bearings at the wrist pin, a larger
wrist pin [ 1” instead of 7/8”] and a full-flow,
spin-on, oil filter as standard equipment.
With some minor differences, this
presentation is also appropriate for the other
Blackmer 1 and 2-stage models, with the
exception of the HD942, double-acting
compressor.
Select one of the following:
Hilites Only
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Detailed Text
HD372 Industrial Compressor
LITERATURE
Have the literature for
your machine at
hand
• Parts lists
• Installation,
Operation and
Maintenance manual
Call your Blackmer
distributor for
literature
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LITERATURE
Be sure that you have the
literature you require before
starting to work on the
compressor. Locate the parts
list and Installation, Operation
and Maintenance instructions.
In addition, you may have
received additional instruction
sheets with your machine that
further describe such items as
valves and packing.
If you do not have all of the
necessary information, call
your Blackmer distributor.
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Tools
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• Use standard tools
for small machines
• Blackmer spanner
(p/n 790535) for
valve hold down
screws
• Blackmer adjustable
spanner with 1/4”
pins (p/n 790316)
• Inside snap ring
pliers
Tools
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Blackmer offers a complete tool kit
which has all of the hand tools
necessary to dismantle the machine.
The tools normally required for
small machine service will be
adequate for the work on an HD
compressor. A small strap wrench is
useful and a good spanner. The
Blackmer p/n 790535 spanner is
used for valve hold down screws.
The Blackmer spanner p/n 790316
has 1/4” pins and is used for piston
removal. A flat scraper and inside
snap ring pliers are also needed.
On larger machines a small hoist
might be needed for one man to do
the job, depending on the
environment. Generally, two men can
handle the disassembly of any
Blackmer machine.
Nameplate
• Model number
• Serial number
• I.D. number
Defines construction
• Oil capacity
• Rod inspection
access
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Nameplate
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On the side of every
Blackmer compressor is a
nameplate which doubles as
an access opening for
inspecting the piston rod.
The nameplate will show
the compressor’s model
number, serial number, ID
number, and oil capacity.
The compressor ID is a
coded number that fully
describes the compressor’s
construction.
Make certain that you have
these identifying numbers
when you call your Blackmer
distributor for parts or service
assistance.
HD372
Flywheel Side
• Two-stage
20 bhp (11 kw )
• Non-lubricated
400-825 rpm
• Reciprocating
air-cooled
• Single-acting
various gases
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HD372
Flywheel Side
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The HD372A is a two-stage, nonlubricated, reciprocating
compressor designed to handle
many different gasses. It is rated
for up to 20 bhp (15kw) and
operates generally between 400825 rpm.
The HD372A is an air-cooled
machine and is normally fitted with
an air-cooled intercooler for the
compressed gas. The intercooler
shroud was removed for these
photos.
Some process application will
require engineered intercooling
systems with heat exchanger and
liquid separation equipment.
These are provided by the
equipment packager as part of an
integrated system.
HD372 Oilpump
Side
• Other Models
Available
Liquid-cooled
HDL372
Smaller HD172
[10 bhp (7.5 kw)]
Larger HD612 and
HDL612
[40 bhp (30 kw)]
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HD372 Oilpump
Side
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Blackmer offers a variety of
two-stage compressors.
The HDL372 is similar to the
HD372 shown in this presentation
but is liquid cooled. It has a
water cooled head and cylinder
for lower metal temperatures and
longer life of wearing parts. It is
also fitted with a water cooled
intercooler to keep gas
temperatures at acceptable levels
for continuous duty.
The smaller HD172 air-cooled
model is rated for 10 bhp (7.5
kw).
The larger HD612 (air-cooled)
and HDL612 (liquid cooled)
models are rated for 40 bhp (30
kw).
Head with
Standard
Suction Valves
The HD372 is a two cylinder
compressor. Each cylinder has
a suction and discharge valve.
These operate automatically and
independently for each cylinder.
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Head with
Suction Valve
Unloaders
• Loadless starting
• Constant speed
operation
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Head with
Suction Valve
Unloaders
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Optional suction valve unloaders
allow the compressor to be
deactivated in service. That is, gas
that is drawn into the cylinder during
the suction stroke is expelled through
the suction valve on the discharge
stroke and does not pas through the
machine into the discharge line. This
is accomplished by holding the
compressor suction valve plates
open throughout the full cycle. The
unloader mechanism does this
mechanically and can be powered by
compressed gas from the discharge
storage or an independent source, as
required.
The suction valves can be
unloaded to produce no-load starts or
reduced capacity operation on
demand.
Removing
Standard
Valves
• Cap O-ring
• Remove hold down
screw from valve
cap
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Removing
Standard
Valves
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Remove the valve caps to
access the valves.
After the valve caps have been
removed, the valve hold down
screws can be removed with a
spanner wrench (such as a
Blackmer p/n 790535).
To prevent possible damage to
the valves during reassembly, the
hold down screws must be
completely removed from the
valve cover plates.
Note the O-ring under each
cap; these should be replaced
rather than reused. The
compressor I.D. number on the
nameplate contains a code for
the O-ring material used.
Valve Cover
Plates
• Replace O-rings
• Reassemble covers
before installing
• the hold down
screws
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Valve Cover
Plates
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Once the valve caps and hold
down screws have been
removed, the cover plates can be
removed.
Note the O-ring under the valve
cover plate. Typically, O-rings are
not reusable and should be
replaced any time the cover
plates are remove.
During reassembly the valve
cover plates must be reinstalled
first, before the hold down screws
are installed.
Valves
• Valve cages
• Valves
• Always replace
gaskets
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Valves
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Once the cover plates
removed, the valve cage, valve
and gasket may be taken out.
Make certain the valve
gaskets are removed with each
valve. When they are left in the
head they may be difficult to
see. The valve gaskets are
normally iron although other
materials are used as required.
Valve gaskets should be
replaced when the valves are
removed.
Removing
Suction Valves
with Unloaders
• O-ring
• Remove hold down
screw from valve
cap
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Removing
Suction Valves
with Unloaders
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Use a strap wrench to remove
the unloader assembly and its
O-ring. Alternately, a bar can be
levered against a pair of
unloader cap screws.
Once the unloader assembly
is removed, the valve hold down
screw can be removed.
When assembling, make sure
the cover plate is firmly secured
before reinstalling the hold down
screw.
Suction Valve
Removal
• Valve cage
• Unloader plunger
• Valve with actuator
• Always replace
gasket
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Suction Valve
Removal
Once the hold down screw is
removed, the cover plate and its
O-ring can be removed. Under
the cover plate is the valve
cage, unloader plunger, suction
valve with unloader actuator,
and a valve gasket.
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Suction Valve
Unloaders
• PTFE Unloader
piston seals
• All Stainless Steel
Parts
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Suction Valve
Unloaders
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The unloader assembly
consists of a cap, body with Oring, and a piston with two
spring loaded PTFE seals. The
open side of the seals should
face outward. The unloader
actuator and spring are held to
the valve with a snap ring.
The unloader cap, body
piston, actuator and spring are
all stainless steel.
Disassembled
Valves
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• Valve components:
seat
bumper
springs
plate
post
nut
lock washers
Disassembled
Valves
A disassembled suction valve
is shown on the left, a discharge
valve on the right.
Each valve consists of a seat,
stop ( bumper ), springs, plate,
threaded post, nut and locking
washers.
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Standard
Intercooler
• Radiator or Finned
tube types
• All steel
construction
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Standard
Intercooler
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The intercooler is readily
unbolted from the cylinder head
at two locations. Note the PTFE
intercooler flange O-rings.
Earlier models were fitted with
the finned tube intercooler as
shown on the right. Standard
intercoolers are all steel
construction and rated for the
first stage discharge pressure.
Cylinder Head
• O-ring head - to cylinder seals
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Cylinder Head
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To remove the cylinder head,
unbolt the two center head bolts
from the top of the head and the
eight head bolts from the bottom
of the head. After the cylinder
head bolts have been removed,
the head may be lifted from the
cylinder. Note that the head is
sealed to the cylinder by an Oring at each cylinder bore.
Piston Removal
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• Remove piston nut
with 1/4 ‘ pin
spanner
• Piston nut has nylon
locking insert
• Use spanner to
unscrew piston
• Washer and shims
adjust piston end
travel
• Piston rings have
expanders
Piston Removal
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The piston nut is removed with an
adjustable spanner. This spanner has
two 1/4” pins which fit into holes in the
top of the piston nut. Note the nylon
locking device on the piston nut.
Once the piston nut has been
removed, the same spanner can be used
to unscrew the piston from the rod.
There is a thick washer under each
piston and one, or more, shims. These
shims adjust the height of the piston in
the cylinder. This is referred to as the
“deck height”. Unless a major part has
been changed, the deck height should
not need adjustment. Change of the
piston, crosshead assembly, cylinder
body, main bearings or crankshaft may
require adjustment of the deck height.
Rotate the crankshaft to bring the
other piston to top-dead-center for
removal. Each piston is fitted with three
piston rings. Each ring has a stainless
steel expander between it and the piston.
Piston and
Cylinder
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• Ring gap is 180o
from expander gap
• Stagger ring gaps
around piston
• Two O-rings
cylinder-tocrankcase
• Under-piston
channel between
bores
Piston and
Cylinder
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When installing he piston rings
and expanders make sure that
each piston ring is installed with
its gap 1800 from the expander
gap. Also, the piston ring gaps
should be staggered around the
piston.
With the pistons removed, the
cylinder can be unbolted and
removed to gain access to the
packing boxes. Two O-rings seal
the bottom of the cylinder.
Notice the passage in the
bottom of the cylinder between
the bores. This allows gas to
move from one cylinder to the
other as the pistons move up
and down.
Packing Box
Removal
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• Remove hold down
screw with spanner
• Hold down screw
has nylon locking
insert
• O-rings seal
packing box at each
end
Packing Box
Removal
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The packing boxes are
secured by a hold down screw
which is removed with the same
adjustable spanner that was
used on the piston nut and
piston. Note that the hold down
screw also has a nylon insert
that keeps it in place.
The packing boxes may now
be lifted off the rod. O-rings seal
the top and bottom side of the
packing boxes.
Packing Box
disassembly
• Depress spring with
screwdriver while
removing retainer
ring
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Packing Box
disassembly
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Remove the seals (packing)
from the box as follows:
Use a pair of inside snap ring
pliers to remove the top snap
ring. A screwdriver handle can
be used to depress the spring to
make this operation easier.
Turn the packing box over to
remove the bottom seal.
Rod Seals
• “V” - ring type
• Spring is next to the
convex surface
• Oil deflector ring
between seals
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Rod Seals
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With the snap ring removed, the
top washer, spring, middle
washer, seal rings, bottom washer
and retainer ring can all be
removed.
The seal consists of three types
of rings. One ring is a male ring,
next a series of V-rings, then a
female ring.
The upper and lower seals are
the same. The seal orientation
will depend on the operating
pressures. The spring and
washer, however, always press
against the male ring.
The red oil deflector ring fits on
the piston rod between the two
seals. The holes in the side of the
packing box allow the oil deflector
ring to be guided onto the rod as
the box is installed.
Piston Rod
Inspection
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• Piston rods and
tops of the
crossheads are
visible through the
nameplate opening
Piston Rod
Inspection
The piston rods and the top
on the crossheads are visible
through the opening when
the nameplate is removed.
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Crankcase and
Crosshead
• Gasket between
crankcase and
guide
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Crankcase and
Crosshead
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By removing the crosshead
guide, access is given to the
crosshead / piston rods.
The flat gasket that fits on
top of the crankcase may
require the use of a flat
scraper to remove
completely.
Oil Pressure
adjustment,
Strainer
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• Oil pressure
adjustment screw
and lock nut
• Clean the oil
strainer
• Oil drain plug
• Oil filter now
standard
Oil Pressure
adjustment,
Strainer
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The oil pressure adjustment
screw complete with O-ring, lock
nut, spring and ball fits into the
bearing carrier. Turning the
screw inward (clockwise)
increases the oil pressure
setting.
The oil pickup tube with
washers, O-ring and strainer fits
in the crankcase under the
bearing carrier. If any foreign
material is noticed in the
strainer, its source should be
quickly identified to prevent
reoccurrence of the problem.
The pipe plug next to the oil
pickup tube opening is the
crankcase oil drain.
Crankcase
Access
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• Access cover and
gasket
• Dipstick
• Remove lower
bearing caps, lift
crosshead and
connecting rod
assembly
Crankcase
Access
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The oil dipstick is located
adjacent to the access cover.
In earlier models, it was
located in the access cover.
The oil viscosity and capacity
are found in the Instruction
Manual.
Removal of the crankcase
access cover and gasket
permits access to the
connecting rods. After the
bottom cap of the connecting
rod has been removed, the
piston rod / crosshead and
the top half of the connecting
rod may be lifted off from
above.
Crosshead and
Connecting
Rod
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• Connecting rod has
cast-in lube
channels, big end
to small end
• Connecting rod is
Ductile Iron
• Crosshead is now
cast iron
• Don’t remove piston
rod from crosshead
Crosshead and
Connecting
Rod
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The connecting rod and
crosshead assembly are separated
by removing the wrist pin in a bench
press. Note that the wrist pin has a
plastic retainer plug on each end.
The piston rod is permanently
secured to the crosshead at the
factory and no attempt should be
made to separate them. Final
machining is done to the assembled
crosshead / rod which precludes
their reassembly once separated.
The grooves in the crosshead are
lubrication channels.
The small end of the connecting
rod shown here has a bronze
bushing. This is used on some
models. Current production for the
HD362, 342 and 372 incorporates a
steel needle bearing in the
connecting rod small end.
Crosshead and
Connecting Rod
(cont’d)
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• Wrist pin is pressed
in or out of the
crosshead
• Wrist pin bushing is
pressed in and honed
to the proper bore
• Bushing oil hole must
align with connecting
rod feed hole
• Some models have
needle wrist pin
bearings
Crosshead and
Connecting Rod
(cont’d)
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The ductile iron connecting rod has
a cast in tube to route oil from the big
end to the wrist pin.
A precision insert split shell bearing
is located at the big [journal] end.
Tabs on the bearing shells fit into slots
in the rod and bearing cap. These
retain the shells and align the oil feed
holes.
The HD372A uses a bronze
bushing on a steel wrist pin at the
small end of the conrod. A steel
needle bearing is used on some
models. The oil admission hole in the
bearing or bushing must align with the
oil supply hole in the connecting rod
small end. When the bronze wrist pin
bushing is replaced, it must be honed
to final dimension after being pressed
into the connecting rod
The rod and cap are matched sets,
do not mix. Match marks must align
when assembling bearing cap to
connecting rod.
Bearing Carrier
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• Carrier and oil pump
are removed as an
assembly
• Slot in carrier fits
into tang at
crankshaft end
Bearing Carrier
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The entire bearing carrier /
oil pump assembly, with
gasket, can be removed
intact. This allows the
crankshaft to be removed.
Note the slot in the end of
the oil pump drive shaft. This
slot must align with the drive
tang in the end of the
crankshaft during installation.
Oil Pump
(HD372A)
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• May be installed for
either rotation
direction
• Rotate cover 180°
for opposite rotation
direction
Oil Pump
(HD372A)
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This photo shows the oil pump
used in the HD372A. Models
HD372B and HD372C use a
different pump.
Remove the oil pump cover
and O-ring to withdraw the oil
pump. Notice the small O-ring
on the pump shaft and the
bronze bushing in the bearing
carrier.
The oil pump cover can be
installed with either left or right
rotation arrow visible. When
installing the cover, make sure
that the arrow at the TOP of the
cover indicates the desired
rotation direction.
Crankshaft
Removal
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• Pressure lubrication
holes at the journal
bearings
• Oil spray nozzles on
the crankshaft for
the crossheads
• Crankcase breather
vent
Crankshaft
Removal
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Remove the crosshead and
connecting rod assemblies to
proceed with the crankshaft
removal. Notice the lubrication
holes on the bearing journals.
Also note the spray nozzles on
the crankshaft. The spray
nozzles lubricate the crosshead
guide and the main [ roller ]
bearings.
The top of the crankcase is
fitted with a breather which
prevents entry of foreign
material into the crankcase but
allows the release of crankcase
pressure.
Bearing Cover
Plate
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• Located at flywheel
end
• Shims adjust main
bearing preload
• Shims are reusable.
Adjusted for new
• main bearing or new
crankshaft
• Cover contains
crankshaft oil seal
Bearing Cover
Plate
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Remove the crosshead and
connecting rod assemblies to
proceed with the crankshaft
removal. Notice the lubrication
holes on the bearing journals.
Also note the spray nozzles on
the crankshaft. The spray
nozzles lubricate the crosshead
guide and the main [ roller ]
bearings.
The top of the crankcase is
fitted with a breather which
prevents entry of foreign
material into the crankcase but
allows the release of crankcase
pressure.
End of Presentation
1809 Century Avenue
Grand Rapids, MI, USA 49503
Ph: 616-241-1611
Fax: 616-241-3752
www.blackmer.com