Work with high-pressure hydraulics involves bending, pushing, lifting or pulling. With hydraulic technology, this work can be done with a degree of precision and control that is not easily achieved with other forms of equipment.
It is accepted that hydraulic power is a safe method of applying force. However, the simplicity of high-pressure hydraulics tools can often lead to their abuse. Like most equipment, there are rules and disciplines to be observed to ensure the safety of other people in the vicinity of the job and the longer life and efficient functioning of the equipment.
STANDARD SAFETY RULES
Before handling high-pressure hydraulic equipment, standard safety rules should be observed. Safety glasses, a hard hat, gloves, safety shoes or boots and protective clothing should be not only the norm in safety apparel but mandatory. These are the basic rules in an often hazardous environment.
When using hydraulic tools and systems, one naturally takes the obvious precautions to avoid mishaps and accidents, improve production levels and to substantially enhance the life of the equipment.
However, most problems encountered in a hydraulic system are the result of improper assembly or operation. Operating instructions should be studied carefully before use, ie know what each function is and how it works.
MAKING THE JOB EASY
An operator should avoid lifting a load that exceeds the capacity of a system. Overloading not only damages cylinders but also blows seals and bends plungers.
The following points should be considered:
? A good rule of thumb is to estimate the load and then double it.
? Remember that some pumps have relief valves while others do not.
? Use a gauge to indicate safe operating loads.
? Before making or breaking any hydraulic connection, make sure there is no pressure in the system. Check the gauge! It could indicate the presence of some pressure.
? Before advancing or retracting a cylinder, it is good practice to make sure the area is clear.
Be familiar also with advances in hydraulic cylinder technology. Enerpac, for example, has introduced to Australasia the next generation of its RC general purpose cylinder family, a widely used, compact, powerful and versatile high-pressure cylinder range.
The GR2 bearing system surrounds the cylinder seal on longer stroke models for ultimate protection. Its innovative design also distributes lateral loads more effectively, increasing cylinder life. The GR2 is designed to withstand lateral forces and dynamic loads, preventing galling and premature bearing failure, keeping jobs on schedule, safely. New heavy-duty return springs with improved retraction rates get the job done fast. And an easy access design requiring only standard shop tools reduces maintenance downtime.
LOOKING AFTER CYLINDERS
Basically, at the working end, there are two types of cylinders: single- and double-acting.
Single-acting cylinders can be either the push type or the pull type and, again, they can be either spring return or load return. Double-acting cylinders are advanced and retracted hydraulically.
There are some specific rules concerning cylinders, eg:
? Always position the cylinder on a firm base of sufficient bearing strength. It would not be amusing to see a hydraulic cylinder disappearing into the soil beneath it. Wherever possible, use a jacking base. If not, use a steel plate or timber to spread the load.
? Avoid point loading on the saddle. Make sure the load is across the entire saddle.
? Keep well clear of areas directly below loads supported by hydraulic cylinders.
? Position cylinders so that the hose and coupler have sufficient clearance when the cylinder extends.
? Keep equipment away from excessive heat; above 65?C will soften packing and weaken hoses. If you use heat, shield the cylinder with a heat-resistant blanket or a piece of metal to deflect the heat.
? Oil connections should be kept clean.
? Couplers should be wiped before connecting.
? Dust caps should be used to keep dirt out, otherwise cylinder walls will be scored, causing seal failure.
? Cylinders should not be over-extended. Not all makes of cylinder have safety stop-rings.
? Cylinder mounting threads should be protected.
? Protectors should be used to prevent damage to the thread.
? Avoid disconnecting extended cylinders and then adding oil to the pump. If there is insufficient space in the reservoir to take all the oil, then the reservoir will become pressurised. It is not a pressure vessel. The end will blow off or the reservoir will rupture.
Pumps are available to match cylinders for all applications, depending upon oil capacity and speed. They can be hand-operated or power-assisted. While hand pumps are used for low-speed applications and where a ?feel? is needed, power pumps are used where higher speeds are needed or when large cylinders are used.
The correct type of pump valve should be used for a particular cylinder. For single-acting cylinders, a pump with a two- or three-way valve (ie one outlet) should be used. For double-acting cylinders, a pump with a four-way valve (ie two outlets) is necessary. (Note: There are dangers in using two-way valves with double-acting cylinders.)
The level of the pump reservoir should be checked before use. The correct filling procedure should be adopted.
The most commonly used system is a hand pump with a single-acting cylinder. The pump can be operated in any position from horizontal to vertical if the hose end is down. If air is in the hose, the cylinder will not move immediately. The cylinder should be bled.
The release valve should be closed, finger-tight, then pumped with firm, full strokes. As pressure increases, the stroke should be shortened to ease the pumping action. If the handle is pulled up hard, it will damage the pump plunger.
Avoid the use of an extension on the pump handle. It will make the pump unstable and will not generate any more pressure if the pump is fitted with a relief valve. Without a relief valve, the system will be pressurised beyond its safe limits and will be dangerous.
With a double-acting cylinder, the control valve handle should be moved toward the hose that you wish to pressurise. It is always useful to understand how oil flows in and out of a cylinder.
Power pumps come in different outputs and power options: air, electric or petrol engine.
A simple way to choose the right size pump is to use a speed selection chart. Make sure the pump has the correct type of valve for the cylinder being used. The pump should be on a firm level base and there should be slack in the hoses because as hoses pressurise they shorten. If there is no slack, the hoses will pull out of the end fittings.
When using a power pump, make sure that all hoses and fittings are connected to the proper inlet and outlet ports of the valve and cylinder. Check that the oil level is correct. The breather should be fully open and the control valve set at neutral before starting the pump. Make sure that all other valves in the system are correctly set.
The pump?s electrical specifications should be checked against the supply voltage. If using an air-operated pump, make sure that the compressed air is clean and lubricated, as dirty air will soon destroy an air motor.
The pump valve should not be relied upon for load holding. Shut-off valves or safety valves should be used where necessary to hold cylinder pressure.
Pump selection guidelines
? Determine appropriate ratings for oil capacity, maximum operating pressure, cycle duration and frequency, flow rate, and valving.
? Compare overall cost. Increased productivity and reduced manpower requirements should be considered.
? Check safety and ease of use. Portability and weight determine how much strength and dexterity the operator must have. Sound levels should be low.
? Match tool speed. As pump size increases, power requirements escalate. Pumps should be sized to the required speed only.
? Check power requirements. Available power dictates the type of pump used.
Be aware of advances in technology. Enerpac?s ZU4 series portable hydraulic pumps feature a 1.25kW universal motor coupled with a new pump element design that reduces oil flow turbulence, producing an instrument with fewer moving parts and less friction. Models can be configured for specific applications, including bolting.
Similarly, the ZE series of 700 bar electric pumps is engineered to save power and increase reliability by reducing its number of moving parts, enhancing flow characteristics and reducing friction.
The high efficiency design of the ZU and ZE series electric pumps have higher oil flow and by-pass pressure, run cooler and require 18 per cent less current draw than other pumps.
HOSES AND COUPLERS
All hydraulic connections, hoses and fittings should comply with the proper pressure rating and be properly tightened.
If PTFE tape is used, it should be applied properly as pieces may enter the system and cause a malfunction. Pipe connections should not be tightened to excess as this can cause thread damage and may split castings.
It is not advisable to carry hydraulic equipment by the hose as this could strain the hose fittings and cause leaks. Sharp bends in the hose should be avoided, as this will damage the internal wire braids.
Heavy objects dropped on the hose could result in hose failure.
Hydraulic couplers should be fully tightened. Loose coupler connections could cause complete or partial blockage of oil flow between pump and cylinder. Dust caps should be fitted to coupler halves when they are disconnected to guard against the entry of dirt or foreign matter that could cause pump or seal failure.
Be careful about hose selection and abuse of hoses. If incorrectly specified, or abused in service, hoses can become the weak point of a hydraulic system, with potentially lethal consequences.
Again, be aware of advances of technology in this area. Enerpac, for example, is introducing new hydraulic hoses engineered to provide ultimate safety in the workplace.
The new Enerpac hoses ? with a MSHA rated abrasion and flame resistant diffusion sleeve ? are suitable for use with all 700 bar (10,000 psi) high-pressure hydraulic equipment and are fully MDG41 Guideline compliant for fluid power system safety at mines. They are designed for safety in heavy or challenging lifting and manoeuvring operations.
The new hoses and the 700 series thermoplastic hoses can be used with Enerpac?s range of hydraulic tools and most other hydraulic tools commonly in use throughout Australia and New Zealand. The 700 series features a four-layer design, including two high-strength steel wire braids and an outside jacket of polyurethane to provide maximum abrasion resistance. The hoses exhibit low volumetric expansion under pressure to enhance overall hydraulic system efficiency.
OILING THE SYSTEM
A system is only as good as the oil it uses. It is advisable to adopt the manufacturer?s recommendations on the type of oil to use. Periodic oil changes are essential. Dirty oil will damage hydraulic systems and make for unsafe conditions. (Precaution: Hydraulic oils contain additives and, as such, skin contact should be avoided.)
GAUGES AND SNUBBER VALVES
Gauges indicate the ?action? of the system, ie what?s going on. These precision instruments should be treated with care, eg releasing the pressure in a system could suddenly cause the needle to snap back, throwing the gauge out of calibration. A snubber valve can prevent this happening. It will also help dampen out any pressure fluctuations, thus giving a more accurate, easy to read pressure or force indication.
ON COMPLETING THE JOB
After using hydraulic equipment, make sure it will be ready for the next time it is needed. The equipment should be cleaned before storage. Wipe it down and lubricate any parts exposed to the atmosphere. Any damage or malfunction should be reported to a supervisor or the equipment should be tagged before re-use.
For effective operation, select the correct size of cylinder, the right pump and the right accessory equipment. Adopting simple safety rules adds to the power and convenience of high-pressure hydraulic tools. When working with such powerful tools, use them properly ? and safely.
Tony Cooper is the engineering and operations manager of the Australasian operations of Enerpac.