Assembling & Pressure Testing


Hydraulic Cylinder Assembling

Ningbo LD has a dust-free clean assembling room with stable temperature control. Assembling operators required to strictly follow assembling drawings during the assembling operating. “ Hydraulic Cylinder Assembling Daily Reports” required to write down by QC Manager.

Pre Assembly Check After Cleaning


Making sure there are no burrs in drilled holes or threads, no sharp free edges. Weld slag, metal chips, dirt etc. should be removed cleaning.


Making sure there is no burrs left in port hole area, 100% ID surface polishing to avoid any contamination, and then cleaning in auto-cleaning machines.


Chrome surface checking, no dings, pits or scratches. Chrome thickness checking to make sure they are qualified to required thickness.


Uniform, sound, free of porosity, inclusions, undercutting Free of splatter and slag.


Ningbo LD never use China Brand seals, all Cylinder seals import from USA, UK, Europe, using good quality Brand. All seals stock in a separate room with stable temperature and humidity control.

During assembling, operators required for visual check or abnormal condition refer to the assembling drawings for proper position and orientation of seals. Ensure installation tools did not cause any damage on sharp edges or surface.

Assembling Room


Pressure Testing Oil Cleanness

1、 Apply pressure, push button marked 'Test Extend'. For safety, hold hose or use tie down while cylinder is extending.
2、 Measure and verify the extended length as per drawing.
3、 When the cylinder is pressured up, check the weld around the end cap and port for leaks, also check around the rod wiper for seal leaks.
4、 When the test is complete, push button marked 'Test Retract'. For safety, hold the hose tie down while cylinder is retracting.
5、 When the cylinder is pressured up, check the weld around the end cap and port for leaks, also check around the rod wiper for seal leaks.
6、 Measure and verify the retracted length as per drawing.
7、 When all tests are successfully completed, push and hold button marked 'Purge Extend'. When the rod is fully extended, repeat the process using 'Purge Retract' button. All cylinders must be in the retracted position when all testing is complete.
8、 Verify the retracted rod orientation as per the drawing requirement.
9、 Disconnect hoses, remove fittings, and roll cylinder over to allow the remaining oil to drain out.
10、 Plug the port holes with proper plugs. Checking the lock nut torque.
11、 QC Manager writes down “ Daily Hydraulic Cylinder Pressure Testing Records”


Oil Cleanliness Testing

Ningbo LD required operators to change or re-clean pressure testing machines’ oil monthly according to the amount testing cylinder quantity.

For some of clients’ cylinders who required higher level of oil cleanness , we will do the oil cleanness testing according to ISO 4406-1999 level.

ISO 4406 Code cleanliness levels are defined by three numbers divided by slashes. These numbers correspond to 4, 6, and 14 micron, in that order. Each number refer to ISO range code, which is determined by the number of particles for that size (4,6 &14 μm) and larger present in 1ml of fluid. Each range is double the range below.