Hydraulic cylinder seal kits are used to seal the gap between different parts of the hydraulic cylinder. The function of hydraulic cylinder seal kits is to prevent oil leakage, to assure the working pressure of the hydraulic system, to maintain its power.
Boom Cylinder seal kit is, as the name suggests, fitted into the boom cylinder.
There are regularly three cylinders for the excavator, boom cylinder, arm cylinder, bucket cylinder.
Arm cylinder is the top one, and it's usually be called as top cylinder;
The bucket cylinder is the one that connects and controls the bucket.
Boom cylinder is the one (or the two) near the cabin. Usually, there is one piece boom cylinder for the small excavator under 10-tun; the bigger excavator's two pieces boom cylinders. But there is an exception too when the driver will remove one piece for a special purpose, say at some particular working place, it is convenient to work by one cylinder. Soft remind: all refit job should be operated by an experienced technician.

The seals in the cylinder seal kit are of two kinds seals.
One call dynamic seals; the other is static seals.

Dynamic seals are designed to be utilized in high pressure and even when rod and hydraulic cylinder seals are in reciprocal motion between the head and the connecting rod. They are to seal various parts in relative motion.

Static seals are the ones used in various loions that not in relative motion, as per the construction and look of the hydraulic cylinder. The primary area where these seals used are the connection rod and piston.

Every type of dynamic seals has its function.

1 liner
2 piston
3 piston rings
4 piston pin
5 main bearing
6 con rod bearing
7 con rod bushing
8 camshaft bushing
9 upper gasket set
10 lower gasket set
11 fuel injector
12 fuel injection pump
13 ECU/ECM
14 nozzle&control valve
15 turbocharger
16 alternator
17 starter
18 water pump
19 lube oil pump
20 fuel transfer pump
21 all sensors
22 thermostat
23 solenoid
24 belt
25 intake/exhaust valve
26 rocker arm
27 push rod
28 gear
29 oil seal
30 cylinder head gasket
31 fuel filter
32 oil filter
33 water filter
34 air filter
35 tensioner
36 idle pulley
37 manifold
38 aftercooler
39 oil cooler
40 air compressor
41 cylinder head
42 cylinder block
43 crankshaft
44 camshaft
45 connecting rod
46 wire harness
47 oil pipe
48 hose
49 oil pan
50 fly wheel