LB361 LPG / NH 3 Compressor. This presentation is a simplified description of the disassembly of a Blackmer LB361. The subsequent model, LB361A, is similar but has an O-ring instead of a flat gasket between the head and cylinder.
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This presentation is a simplified description of the disassembly of a Blackmer LB361. The subsequent model, LB361A, is similar but has an O-ring instead of a flat gasket between the head and cylinder.
The current production model is the LB361B (August 1997). The largest difference affecting disassembly is in the oil pump. The current oil pump is self reversing and is not shown in this presentation
Select one of the following:
The LB361 compressor is suitable for many applications, but the most common is the transfer and vapor recovery of liquefied gases such as propane, butane, and anhydrous ammonia. The non-lubricated cylinder design of the LB361 allows the transfer of these products without contamination of the products and is capable of transferring up to 200 gallons per minute (760 lpm). Typically the LB361 is driven by a 10 or 15 HP driver in the 650 to 800 rpm range.
Be sure you have the proper literature before starting 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.
Literature is available on the web at:
or from your Blackmer distributor.
The tools normally required for small machine service will be adequate. A small strap wrench is useful as well as a good spanner. 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.
Blackmer offers a complete tool kit which has all of the hand tools necessary to dismantle the machine.
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.
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.
Blackmer offers a variety of LPG transfer compressors.
The LB362 is similar to the LB361 shown in this presentation but has two seals separated by a distance piece on each piston rod.
LB161 / LB162 [7.5 bhp (5.5 kw)]
LB601 / LB602 [40 bhp (30 kw)]
LB942 [50 bhp (37 kw)]
Blackmer compressors are typically fitted with a pressure gauge on both the suction and discharge. The gauges are fitted with a pulsation dampener to eliminate much of the vibration of the gauge needle making it easier to read and extending the life of the pressure gauge.
Both suction and discharge pressure gauges should be installed on every compressor.
Remove the valve caps to access the valves. Note the metal gasket under each cap; these should be replaced rather than reused.
After the valve caps have been removed, the valve hold down screws can be removed with a 3/8” Allen wrench. To prevent possible damage to the valves during assembly, the hold down screws must be completely removed from the valve cover plates.
Once the valve caps and hold down screws have been removed, the cover plates can be removed. Note the the O–ring under the Cover Plate. These O-rings should be replaced, not reused any time the cover plates are removed.
During assembly, the valve cover plates must be installed first, then the hold down screws installed.
With the cover plates removed, the valve spacers, valves and gaskets may be taken out.
A liquid relief device in the suction valve post helps protect the compressor in case liquid enters the cylinder area. It consists of a ball and spring relief valve which will allow liquid to be returned to the suction piping if necessary.
The discharge valve is held in place by a solid post.
Make certain the metal valve gaskets are removed with each valve as they may be difficult to see in the head. The valve gaskets are normally aluminum and must be replaced when the valves are removed.
To remove the cylinder head, unbolt the two center head bolts from the top of the head and the six head bolts from the bottom of the head.
The two center head bolts on models with flat head gaskets have metal gaskets which are normally not reusable.
After the cylinder head bolts have been removed, the head may be lifted from the cylinder.
The LB361 head is sealed to the cylinder with a flat head gasket. Carefully use a flat scraper or putty knife to remove the old gasket material before installing a new one.
The LB361A and LB361B use O-rings to seal the cylinders.
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 spanner is used to unscrew the piston from the rod. Under each piston is a thick washer 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. Changing 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. Install each piston ring with the bevel on the inside facing up. The ring and expander gaps should be staggered at 180° intervals during installation.
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.
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 bottom side of the packing boxes.
To remove the seals (packing) from the box:
Remove the top snap ring with a pair of inside snap ring pliers. Depress the spring with a screwdriver handle to make this operation easier.
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.
On LB361 compressors, the spring and male ring will be at the top and the female ring will be at the bottom.
The piston rods and the top on the crossheads are visible through the opening when the nameplate is removed.
The crosshead guide is secured to the crankcase by six bolts.
With the crosshead guide removed, the crosshead / piston rods are visible. The flat gasket on top of the crankcase may require the use of a flat scraper to remove completely.
The oil dipstick is located in the access cover. On current models, it is located adjacent to the access cover. The oil viscosity and capacity are found in the Instruction Manual.
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 has a bronze bushing and is lubricated via and internal port running the length of the connecting rod.Crosshead and Connecting Rod
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 LB361 uses a bronze bushing on a steel wrist pin at the small end of the conrod. 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.
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.
Some units will be fitted with an external oil filter (not shown).Oil Pressure adjustment, Strainer
This photo shows the oil pump used in the LB361 and LB361A. The LB361B uses 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.
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.Bearing Carrier
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.Crankshaft Removal
Liquid transfer / vapor recovery of:
Transfer without contamination
Up to 200 GPM
Usually driven by 10 or 15 HP driver at 650 to 800 rpm
Have the proper literature at hand
Installation, Operation and Maintenance manual
Call your Blackmer distributor
Use standard tools for small machines
Blackmer adjustable spanner with 1/4” pins (p/n 790316)
Inside snap ring pliers
Blackmer tool kit available
Other Models Available:
[7.5 bhp (5.5 kw)]
LB601 / LB602[40 bhp (30 kw)]
LB942 [50 bhp (37 kw)]
Suction & Discharge
Pulsation dampener- extends gauge life & makes it easier to read.
Cap gasket (metal)
Remove screws with 3/8” Allen wrench
Remove screw completely from cap!
Liquid relief device - ball & spring
Valve gaskets - usually aluminum
Always replace gaskets
Two center head bolts have metal gaskets
Six bolts from the bottom
Head Gasket (LB361)
(LB361A & LB361B)
Remove old gasket material!
Remove piston nut with 1/4” pin spanner
Piston nut has nylon locking insert
Use spanner to unscrew piston
Washer and shims adjust piston deck height
Piston rings have expanders
Bevel on inside of the ring faces up
Install rings and expanders with staggered gaps
Two O-rings seal the cylinder to the crankcase
Under-piston channel between bores
Remove hold down screw with spanner
Hold down screw has nylon locking insert
O-rings seal bottom of packing box
Depress spring with screwdriver
Remove retainer ring with inside snap ring pliers
Female packing ring on bottom
“V” - ring type
Male packing ring on top
Spring is on top of the packing
Piston rods and tops of the crossheads are visible through the nameplate opening
Gasket between crankcase and guide
Oil level dipstick
Wrist pin is pressed into the crosshead
Wrist pin bushing is pressed in and honed to the proper bore
Bushing oil hole must align with connecting rod feed hole
Split bearings on the crankend
Keep rod caps on the correct rod - use match marks
May be installed for either rotation direction
The top arrow indicates rotation direction
Rotate cover 180° for opposite rotation direction
Oil spray nozzles on the crankshaft for the crossheads
Crankcase breather ventCrankshaft Removal