№

Defect

Possible cause

1

The pump does not supply liquid to the system

Incorrect direction of rotation of the pump shaft

There is not enough working fluid in the tank

The suction line is clogged

Air suction in the suction pipe

Pump failure

The viscosity of the liquid is high

The overflow valve damper is clogged

2

The pump does not generate pressure in the system

The pump does not supply liquid to the system

High wear of the pump (internal leakage is large)

High external leakage along the shaft through the pump housing

High internal leaks in the hydraulic system

The safety valve spool or overflow valve is jammed and cannot be installed on the seat

Reduced oil viscosity due to heating (usually above 50 C)

3

Noise and vibration in the system

High resistance in the suction line

The filter throughput is low or it is clogged

Air suction in the suction pipe

The breather in the tank is clogged

Valve vibration

A sharp change in the flow section of pipelines

Non-rigid fastening of pipelines

4

Unequal movement of working bodies

Air in the hydraulic system 

The pressure setting of the safety valve is close to the pressure required for the movement of the working units

Low back pressure on the cylinder drain

Mechanical jamming of the moving parts of the hydraulic cylinder. Uneven oil supply by the pump. Noise and knocking in the pump due to failure of one of the blades or plunger

5

A sharp decrease in speed when the load increases

Large internal or external leaks in hydraulic system elements

The speed controller jams in the open position

The safety and bypass valves are adjusted for low pressure

6

Gradual decrease in the speed of movement of the working body

Contamination of the working fluid

Clogging of filters, throttles and other devices of the system. The obliteration (overgrowth) of cracks of the throttle

The sealing surfaces of hydraulic units were worn out or the viscosity of the working fluid decreased

7

Increased pressure in the discharge line at idle

Increased pressure losses in the system due to the wrong choice of equipment, reduced cross-section of pipelines, as well as as a result of poor-quality installation

The control channel of the distributor overflow valve is clogged

Increased mechanical resistance to movement of working bodies

8

Increased heating of the oil in the system

Increased pressure losses in pipelines and hydraulic equipment. Low heat removal from the tank and pipelines

The pump does not unload during pauses

Malfunction of temperature control equipment

9

The check valve allows the liquid to flow when the flow direction changes

The valve does not fit the seat. Defect in the working edges of the valve or seat. The valve spring broke

10

The safety valve does not hold the pressure

The damper or valve seat is clogged. Loss of tightness in the remote discharge system

The ball or seat is worn out

A spring broke

11

There is no pressure behind the pressure reducing valve

The damper or valve seat is clogged

The ball or seat is worn out

A spring broke

12

There are large leaks through the drainage holes

Seals were worn out

The working surfaces of mobile switchgears were worn out

13

The electrohydraulic control spool does not switch when the electromagnet is switched on

Jamming of the spool in the housing (the spool teaser). Spool jamming with dirty oil or a sagging return spring. Thick oil makes it difficult to move the spool

The armors of the electromagnets do not move at full stroke

The end of the pusher has splintered

The drain hole in the spool is clogged

14

The electromagnets are humming and overheating

See paragraph 13

The recoil springs are too strong

The supply voltage does not match the nominal value

The armature of the electromagnet has been loosened

15

Breakage and cracks of oil pipelines with changes in sealing

Unacceptable deformations of flexible hoses

Aging and wear of flexible hoses

Resonant vibrations of pipelines

Significant pressure peaks in the hydraulic system

16

The pressure reducing valve does not lower the pressure or does not lower enough

The control spring is compressed almost to the full fit of the coils. The valve spool is jammed. The oil discharge line after the ball into the tank is clogged. The control spring has settled. The damper hole of the spool is clogged. There is dirt between the ball and the seat or the ball is damaged

17

The feed rate of the power unit is low and falls under load (controlled by the flow regulator)

The throttle gap is clogged. The spring of the integrated pressure reducing valve is loose or the spool is stuck

Increased leakage in the pump and hydraulic units

High oil viscosity

18

The oil flow is not reversed by the inlet spool

Jamming of the spool in the housing due to dirty oil, clamping of the mounting bolts, flatness of the mounting surface, breakage of the return springs, lack of control pressure

The pushrod of the control spool’s electromagnet was lost. The coil burned or the anchor broke

19

Oil and foam are ejected through the filling neck of the oil tank or the lid of the built-in drain filter

Excess oil in the tank.

Air intake to the hydraulic system

The filter is clogged or the filter cover seals are damaged. There is no retarding valve on the cylinder drain