Troubleshooting Guide

Hydraulic Pumps
Failure Possible Cause Remedy
Pump noisy

  1. No or insufficient oil supply to pump.
  2. Viscosity of oil too high.
  3. Pump takes in air.
    • at the pump shaft
    • at loose or damaged suction line
    • oil level too low
    • oil takes in air in the tank (return
      pipe discharging over oil surface)
  4. Pump worn out.
  5. R.p.m. too high.
  6. Oil pressure too high.

  1. Clean suction filter. Check that no damage or narrowing is to be found on suction line.
  2. Change the oil, adjust viscosity to working temperature.
  3. Replace shaft seal. Tighten fittings or replace suction line. Refill with clean oil. Extend return pipe to 54 cm under the surface and as far as possible from the suction pipe.
  4. Repair or replace pump.
  5. Adjust the r.p.m.
  6. Adjust oil pressure.
No pressure

  1. Oil level too low.
  2. Pump does not run or runs in the wrong direction.
  3. Relief valve is stuck in open position.
  4. Pump defective, broken shaft or key for rotor.

  1. Refill with clean oil.
  2. Adjust direction of rotation. Check driving belt or coupling.
  3. Repair relief valve.
  4. Repair pump.

No or unstable pressure

  1. Working pressure too low.
  2. Leaky pressure adjusting valve or pilot valve.
  3. The oil flows more or less to the tank through defective valve or cylinder.

  1. Check the pressure adjusting valve.
  2. Repair valve.
  3. Repair cylinder or valve.

Noise in the relief valve

  1. Excessive flow.
  2. Dirt or chips between cone and valve seat.

  1. Fit a larger valve corresponding to the actual oil volume
  2. Repair valve.

Air in the system, foam in the oil

  1. Leaky suction line.
  2. Excessive resistance in suction line.
  3. Return line discharges above the oil level - could cause foam formation.
  4. Incorrect oil type.

  1. Retighten or replace pipe.
  2. Clean filter and suction line, or replace with pipes having larger bores. Check fittings.
  3. Remove return line from suction line and extend if necessary.
  4. Change over to correct oil type.

Overheated system

  1. No supply of cooling water.
  2. Oil cooler blocked or dirty.
  3. Excessive oil viscosity.
  4. Abnormal internal leakage in one or more components.
  5. Altered running conditions.
  6. Pump, valves or motor overheated.

  1. Re-establish supply of cooling water.
  2. Clean oil cooler.
  3. Change over to correct oil type.
  4. Repair or replace defective components.
  5. Establish extra cooling if necessary.
  6. Reduce load or replace component with a bigger one.



BACK to the top


Hydraulic Motors
Failure Possible Cause Remedy
R.P.M. of motor lower than rated value

  1. Pump worn out.
  2. R.p.m. of pump too low.
  3. Motor worn out.
  4. Oil temperature toohigh (resulting in excessive internal leakage in motor, valves etc.) Possibly too high ambient temperature.
  5. Insufficient diameter in pipes etc.
  6. Pump cavitation.
  7. Opening pressure of pressure relief valve too low.
  8. Leaky control valve.
  9. Overloaded motor.

  1. Repair or replace pump.
  2. Adjust the r.p.m.
  3. Repair or replace motor.
  4. Build in oil cooler or increase existing cooler or tank capacity. If necessary change over to oil with a higher viscosity.
  5. Fit lines with larger diameter.
  6. (See under: Pump noise).
  7. Adjust to correct pressure.
  8. Repair valve.
  9. Eliminate the cause of the overload or change over to larger motor.

Motor shaft does not rotate

  1. Pump does not run or runs in the wrong direction.
  2. Motor spool has seized in housing.
  3. Cardan shaft or spool broken (shaft and commutator valve in two).
  4. Working pressure too low.
  5. Sand, steel chips or similar impurities in motor.

  1. Start pump or reverse direction of rotation.
  2. Replace complete shaft and housing.
  3. Replace cardan shaft or complete shaft and housing. Eliminate external forces which caused the fracture.
  4. Adjust operating pressure of relief valve to higher value, however, within permissible limits. If necessary, change over to a motor with higher torque.
  5. Clean the motor, and flush system thoroughly. Renew defective parts. Use a better filtrt.

Motor shaft rotates in the wrong direction

  1. Oil lines are wrongly connected to motor parts.
  2. Gear-wheel and rotary valve incorrectly fitted.

  1. Change the connection.
  2. Adjust settings.

Leakage at motor shaft

  1. Shaft seal worn out.

  1. Replace shaft seal.

Leak between motor spigot and housing

  1. Spigot is loose.
  2. O-ring defective.

  1. Tighten screws with prescribed torque.
  2. Replace O-rings.

Leaks between housing, spacer plate, gear wheel set and end cover, respectively

  1. Screws loose.
  2. O-rings defective.
  3. Steel washers defective.

  1. Tighten screws with prescribed torque.
  2. Replace O-rings.
  3. Replace steel washers.



BACK to the top


ELECTRIC MOTOR HORSEPOWER

Required to drive a hydraulic pump
PUMP PRESSURE PSI
GPM 100 200 250 300 400 500 750 1000 1250 1500 2000
1/2
1
1-1/2 		.04
.07
.10 		.07
.14
.21 		.09
.17
.26 		.10
.21
.31 		.14
.28
.41 		.17
.34
.52 		.26
.52
.77 		.34
.69
1.03 		.43
.86
1.29 		.52
1.03
1.54 		.69
1.37
2.06
2
2-1/2
3 		.14
.17
.21 		.28
.34
.41 		.34
.43
.52 		.41
.52
.62 		.55
.69
.83 		.69
.86
1.03 		1.03
1.29
1.54 		1.37
1.72
2.06 		1.72
2.15
2.57 		2.06
2.58
3.09 		2.75
3.43
4.12
3-1/2
4
5 		.24
.28
.34 		.48
.55
.69 		.60
.69
.86 		.72
.82
1.03 		.96
1.10
1.32 		1.20
1.37
1.72 		1.80
2.06
2.57 		2.40
2.75
3.43 		3.00
3.43
4.29 		3.60
4.12
5.15 		4.81
5.49
6.86
6
7
8 		.41
.48
.55 		.82
.96
1.10 		1.03
1.20
1.37 		1.24
1.44
1.65 		1.65
1.92
2.20 		2.06
2.40
2.75 		3.09
3.60
4.12 		4.12
4.81
5.49 		5.15
6.01
6.86 		6.18
7.21
8.24 		8.24
9.61
11.0
9
10
11 		.62
.69
.76 		1.24
1.37
1.51 		1.55
1.62
1.89 		1.85
2.06
2.27 		2.47
2.75
3.02 		3.09
3.43
3.78 		4.63
5.15
5.66 		6.18
6.86
7.55 		7.72
8.58
9.44 		9.27
10.3
11.3 		12.4
13.8
15.1
12
13
14 		.83
.89
.96 		1.65
1.79
1.92 		2.06
2.23
2.4 		2.47
2.68
2.88 		3.30
3.57
3.84 		4.12
4.46
4.81 		6.18
6.69
7.21 		8.24
8.92
9.61 		10.3
11.2
12.0 		12.4
13.4
14.4 		16.5
17.8
19.2
15
16
17 		1.03
1.10
1.17 		2.06
2.20
2.33 		2.57
2.75
2.92 		3.09
3.30
3.50 		4.12
4.39
4.68 		5.15
5.49
5.83 		7.72
8.24
8.75 		10.3
11.1
11.7 		12.9
13.7
14.6 		15.4
16.5
17.5 		20.6
22.0
23.3
18
19
20 		1.24
1.30
1.37 		2.47
2.61
2.75 		3.09
3.26
3.43 		3.71
3.91
4.12 		4.94
5.22
5.49 		6.18
6.52
6.86 		9.27
9.78
10.3 		12.4
13.0
13.7 		15.4
16.3
17.2 		18.5
19.6
21.6 		24.7
26.1
27.5
25
30
35 		1.72
2.06
2.40 		3.43
4.12
4.81 		4.29
5.15
6.01 		5.15
6.18
7.21 		6.86
8.24
9.61 		8.58
10.3
12.0 		12.9
15.4
18.0 		17.2
20.6
24.0 		21.5
25.7
30.0 		25.8
30.9
36.0 		34.3
41.2
48.0
40
45
50 		2.75
3.09
3.43 		5.49
6.18
6.86 		6.86
7.72
8.58 		8.24
9.27
10.3 		11.0
12.4
13.7 		13.7
15.4
17.2 		20.6
23.2
25.7 		27.5
31.0
34.3 		34.3
38.6
42.9 		41.2
46.3
51.5 		54.9
61.8
68.6
55
60
65 		3.78
4.12
4.46 		7.55
8.24
8.92 		9.44
10.3
11.2 		11.3
12.4
13.4 		15.1
16.5
17.8 		18.9
20.6
22.3 		28.3
30.9
33.5 		37.8
41.2
44.6 		47.2
51.5
55.8 		56.6
61.8
66.9 		75.5
83.4
89.2
70
75
80 		4.81
5.15
5.49 		9.61
10.3
11.0 		12.0
12.9
13.7 		14.4
15.4
16.5 		19.2
20.6
22.0 		24.0
25.7
27.5 		36.0
38.6
41.2 		48.0
51.4
54.9 		60.1
64.3
68.6 		72.1
77.2
82.4 		96.1
103.0
109.8
90
100 		6.18
6.86 		12.4
13.7 		15.4
17.2 		18.5
20.6 		24.7
27.5 		30.9
34.4 		46.3
51.5 		61.8
68.6 		77.2
85.8 		92.7
103.0 		123.6
137.3

This chart is based on the formula HP=
For the purpose of this chart pump effeciency was assumed to be 85%.
As horsepower varies directly with flow or pressure, multiply proportionately
to determine values not shown.
For instance, at 4000 PSI multiply 2000 PSI values by 2.



BACK to the top