Excess heat is generated
1. Internal leakage in the pump increases.
Repair or replace the pump because its volumetric efficiency is deteriorated.
2. Internal leakage in the valve increases.
Repair or replace the valve.
3. Internal leakage in the actuator increases.
Repair or replace the actuator.
4. The sliding part of the pump is seized up (scoring).
Repair or replace the pump.
5. The pump or bearing is seized up.
Replace the bearing.
6. The working fluid in the reservoir is insufficient.
Add the fluid or place a larger reservoir.
7. Oil cooler selection is improper.
Replace the oil cooler with a new one with a larger heat-exchange capacity.
8. The oil cooler performance is inadequate.
1. Check the water temperature and volume and take an appropriate action.
2. Overhaul the cooler and remove water strains and other contaminants.
3. Clean the radiator of the fan cooler.
9. The cooling water in the oil cooler is insufficient.
a. The water solenoid valve is not in working order.
b. The automatic water supply valve with a temperature detector is not in working order.
c. The thermostat is not in working order.
Check whether the temperature difference between the cooling water inlet and outlet is proper. Check and repair the valves and electric systems to make sure that cooling water flow is increased.
10. The heater is not in working order.
Check and repair the heater and thermostat.
11. The unload circuit is not in working order.
a. The unload set pressure is too high.
b. Pressure setting is improper, resulting in a shortened unloading time.
c. The accumulator is not in working order, or its capacity is insufficient.
d. Gas pressure of the accumulator is low.
e. The pressure switch is not in working order.
1. Check and repair the valves.
2. Correct the pressure setting.
3. Replace the failed components.
4. Check and repair the electric systems.
12. The viscosity of the working fluid is low, resulting in increased leakage.
Replace the working fluid.
13. The set pressure level is too high.
Correct the pressure setting to an appropriate level.
Pump produces noise (aeration)
1. Suction pipe connection is loose.
Fix the connection (screwed part and packing).
2. There are foams in the reservoir.
1. The oil level is low: add the working fluid to the recommended level.
2. The reservoir is equipped with no baffle plate, or the reservoir is too small: install an defoaming filter or replace the reservoir
3. Air is leaking in through the shaft seal.
Replace the shaft seal.
4. Air is not completely bled from the casing.
Run the system with no load until air is removed completely.
5. There are bubbles in a line.
Set up an air bleeding circuit for a closed line.
6. The pressure is beyond the specified level.
Drive the pump at or below the specified pressure.
7. A coupling produces noise.
Align the shaft or replace the coupling.
8. Pump parts are worn or damaged.
Repair or replace the parts.
The pump produces noise (cavitation)
1. The suction line or the suction filter is clogged.
Remove the clogging.
2. The suction line is too narrow or long.
Replace the piping so that the vacuum level is kept below the specified value.
3. The capacity of the suction filter is insufficient.
Replace the filter with a new one whose capacity is twice or more as large as the pump discharge flow.
4. The pump is placed too high.
Decrease the suction height (head).
5. The capacity of the boost pump is insufficient.
Repair or replace the boost pump.
6. The working fluid is too viscous to flow into the pump.
Replace the fluid or heat it with a heater.
7. The pump rotation speed is beyond the specified level.
Drive the pump at the specified rotation speed.
8. The air breather in the reservoir is clogged.
Clean the breather.
The pump does not discharge the working fluid
1. The rotation direction is incorrect.
Make sure that the direction is correct.
2. The pump shaft is not rotating.
Check and modify the shaft key and coupling.
3. The suction filter is clogged.
Remove the clogging.
4. Air is in the suction line.
Fix the pipe connection (screwed part and packing).
5. The working fluid is too viscous to flow into the pump.
Replace the fluid or heat it with a heater.
6. The pump is placed too high.
Decrease the suction height (head).
7. The pump rotation speed is too low.
Drive the pump at the specified rotation speed.
8. The amount of the fluid in the reservoir is insufficient.
Add the fluid to the recommended level.
9. Air is not bled at the pressurized side; suction cannot take place.
Take the air out of the highly pressurized line by loosening the line.
10. The variable displacement pump is improperly adjusted.
Check and correct the adjustment.
11. Parts are worn or damaged.
Repair or replace the parts.
Cautions on Piping and Assembling
A hydraulic unit may incorporate steel pipes, stainless pipes, or hoses.
Nominal size of pipes: A (millimeter) and B (inch), outer diameter is same. Scale A (millimeter) is usually applied to pipes for flareless fittings.
Schedule: it refers to wall thickness and is denoted as Sch. See Tables 12.2 and 12.3 for pipe selections in accordance with the working pressure.
•Cautions on Piping and Assembling
i . Use Teflon tape for thread sealing.
ii . Remove burrs and chips after cutting the pipe and threading. Avoid using dull cutting tools and dies.
iii. Make sure that the curvature radius of a pipe is 2.5 to 3 times larger than its inner bore.
iv. Use pipe cramps to eliminate shocks and vibrations, if necessary.
v . Attention should be paid to the following points when a flexible hose is applied.
a) The curvature radius is greater than the specified minimum radius
b) A hose is not twisted.
c) Extra hose length is required because the hose expands with increased inner pressure.
Manifold
Manifolds connect ports of hydraulic components with drilled metal blocks, instead of piping. They usually have outlet ports with tapered threads (Rc) or connection flanges. Manifolds have the following advantages.
i . They can reduce leakage and vibrations with simple piping.
ii . They are compact.
iii. Their assembly does not require trained skills; installation is easy and quickly completed.
iv. Base blocks of 1/8- and 3/8-inch bores have been standardized for modular valves.
Manifolds are made of the following materials.
i . SS material: Often selected for customized units.
ii. SUS material: Used when rust should be prevented.
iii. SF (forging) material: Employed for high pressure applications.
iv. Continuous casting material: Chosen with consideration to cost performance.
v. Aluminum material: Used for light weight applications, such as vehicles.
Selection of Reservoir Capacity
(1) Selection Based on Pump Output Capacity
Generally, reservoir capacity should be three to five times larger than the pump output capacity. In a closed circuit, the reservoir capacity can be about 50 percent of the pump output capacity.
(2) Selection Based on Oil Level Variation
The amount of oil in a reservoir fluctuates with actuator operation. The reservoir should have return and suction lines where the oil can be kept, regardless of oil level fluctuations. Capacity that is three times larger or more than the minimum oil level is generally recommended.
(3) Selection Based on Heat Radiation Area
Heat generated by hydraulic equipment is radiated from the reservoir surface. The recommended reservoir size is, therefore, determined by the presence of a heat exchanger.
(4) Selection Based on Space of Reservior Top
For mounting of a pump, a motor, and valves on the reservoir top, the space of the reservoir top should be taken into consideration.
(5) Compliance with the Safety Laws
The law stipulates that empty space in a reservoir must be equal to or less than ten percent of the reservoir capacity in Japan.
Figure 12.1 shows an example of a hydraulic unit containing a pump, a motor, and control valves. The figure also shows names of optional components and settings.
Requirements for Hydraulic Reservoirs
(1) A reservoir should be set up with a method to shut out foreign substances such as dust. Example: Filter at a ventilation or a filling port.
(2) A reservoir should be set up so that its components can be easily detached for smooth maintenance.
(3) A reservoir should have an oil level gauge for safety.
(4) A baffle plate should be placed between the return and suction pipes to prevent foreign substances from being drawn back through the hydraulic system.
(5) Return and suction lines should be installed below the oil level.
(6) A side cover should be included in a reservoir to facilitate the inner coating and cleaning processes.
(7) Safety Laws (for ex. Fire Service Law in Japan), where applicable, regulates the following items: empty space in the reservoir, level gauge type, and the oil pan volume, etc. Applicable ordinances and regulations depend on the operating pressure and the flash point of the working fluid. Local laws and regulations may also be applicable. For local regulations, their applicability should be checked in advance with the local fire departments and system users.
Fittings
Screw, flange, welded, flare, and flareless fittings are available for line connection and equipment setup. In addition, the following fittings are among the available selection.
(1) Socket: Connects lines into straight configurations. Fittings that connect lines with different bores are called reducer.
(2) Elbow: Changes directions of lines. Elbow fittings for lines with different bores are also available. 90- degree elbows and 45-degree elbows are among the available selections.
(3) Tee (tees): Branches out or in lines.
(4) Nipple: Has male threads at both end to connect lines into straight configurations.
(5) Bush: Has a male and female thread at each end to connect lines into straight configurations. They are usually adapted for lines with different bores.
(6) Cap: Closes the male thread port.
(7) Plug: Closes the female thread port.
(8) Union: Uses screw caps to allow easy disconnection of lines. It is equipped with packing like O-rings.
(9) Flange: Seals line connection with O-rings and tightens it with bolts. It is most generally used for fitting.
The following flanges are available in the inserted welding and butt welding types.
i . JIS-compatible high-pressure rectangular flange
ii. SAE-compatible oblong flange (hexagon)
iii. JIS-compatible low-pressure sphere flange
Rotary Joints
This joint transmits working fluids to rotary parts. The rotary and swivel types are available.
