Truck dumper maintenance
November 01, 1995
by Teresa Acklin
Keeping truck dumping systems in good repair is the key to trouble-free operation.
By WALTER GEISLER and CHARLES CRESAP
The first truck dumper, as we know it today, was air operated and built in 1934. It had two large air cylinders and was 10 meters long by just under 3 meters wide. In 1947, the first hydraulic truck dumper was built.
Truck dumpers are normally about 3 meters wide, and the length varies from 9 meters to 24 meters. The angle of tilt ranges from 28° to 65°; dumpers for free flowing materials such as grains are usually 35° or less, while dumpers for materials such as peanuts, cottonseed and potatoes are 43° to 45°. Angles for more solid goods such as wood products are from 50° to 65°.
There are basically two different types of dumpers: a grade level and pit type. The grade level has cylinders mounted on the side by using an A-frame or trunion mount. The pit type has cylinders mounted under the frame in a deep pit.
The advantage of a grade level type is the cylinders are out where they can be seen and checked daily without any difficulty, whereas on the pit type dumper, the cylinders cannot be seen unless the dumper is raised. Also, in some locations there are water problems which would have an effect on pit cylinders.
The pivot hinge supports the dumper at the pit end while being raised or lowered. It consists of the pivot shaft, platform casting and wall casting (sometimes referred to as pillow blocks). The platform castings are secured to the frame by either four or six bolts. The wall casting sits on the concrete pier and is secured by four or six bolts. On some dumpers the pivot shaft is approximately 3.5 meters long. Others use two short shafts approximately 76 centimeters long.
There are two ways of keeping the truck on the platform while being raised. On dumpers that have a tilt of 45° or less, a wheel stop is used. On dumpers that have a tilt of 45° or greater, a back stop is used. Wheel stops catch the rear tires on the trailer or truck, and back stops catch the frame. In some cases, a back stop is used on dumpers with a tilt of 45° that are used for dumping vegetables. On dumpers over 45° of tilt, the platform must have a front axle or trailer tie-down.
On most dumpers, the wheel stop is one piece that goes across the platform and has one hydraulic cylinder mounted in the center. Chains on stop bars are used to hold the wheel stops when a truck is against them. When chains are used, there are normally four.
A few things should be kept in mind regarding the proper care and precautions to be taken in the use of hydraulic fluids in system operation. Helpful procedures result in less downtime and increased service life as well as higher system efficiency.
Type. A good industrial hydraulic oil should be used. Oil should have an ISO rating of 32 if the system is not a continuous operation. For a system that is running at a constant pressure, an ISO rating of 46 or 68 can be used, as this oil has a higher viscosity rating.
Water. Water in oil causes many types of problems, including internal rusting of cylinders, piping and pumps. Rust flakes can break loose from the piping and damage seals and O-rings and can cause valves to malfunction. Water problems are similar to those with too-heavy oil. Oil with water in it has a milky look to it.
Changed oil. Oil in most hydraulic systems needs to be changed every two years or as required due to contamination. To just change the oil and not clean the inside of the reservoir is defeating the purpose of changing the oil. If the reservoir is not cleaned, the sediment on the bottom will be stirred up and will mix with the new oil the first time the system is used. On units with large cylinders, the cylinders have anywhere from 38 to 190 liters of oil that stay in the cavity of the cylinder in the full collapsed position. This should be drained out to prevent the new oil from being contaminated.
For efficient operation of equipment, it is especially important to keep the hydraulic fluid clean and cool. Contamination is probably by far the greatest source of trouble in the hydraulic system. Work energy lost through excessive generation and dissipation of heat also can substantially reduce system effectiveness while causing oxidation and producing other ill effects.
Grit and metal particles score working parts. Water helps create rust particles, which are abrasive in the system. Furthermore, fluid oxidation in combination with dirt and water forms harmful sludge and varnishes.
In the field of hydraulics, the importance of keeping hydraulic fluid clean and free of contamination cannot be over-emphasized. Foreign matter in hydraulic fluid can create excessive wear, increased power loss and clogged control elements, resulting in erratic circuit performance and substantially increasing replacement and maintenance costs.
A good preventive maintenance program is least expensive and most effective. Regular and frequent inspections at specified points will help prevent breakdown.
One of the biggest problems for grain storage operators is grain spillage that runs under the dumper. If this area is not kept clean, excessive build-up can create an uplift on the hinge, which can cause foundation bolt failure.
Things like leaks, fluid level and condition of the hydraulic fluid can be determined by visual inspection. Excessive pump wear is usually evidenced by gradual increase in cycle time. Plugged suction filters can usually be spotted by pump sound. Fluid temperature above normal always warrants investigation.
In short, hydraulic equipment almost always gives a warning of trouble before breakdown occurs. But someone must note the symptoms and do something about them if the warnings are to do any good.
Always use the best hydraulic fluid available. Keep it in good condition and change it as necessary.
Take advantage of the service facilities made available by hydraulic manufacturers in overcoming any difficulties the maintenance force is not equipped to handle.
Filter elements should be cleaned or replaced by planned periodic inspection. Experience will indicate check intervals.
Efficient operation of hydraulic systems pays substantially. Contributions to this end can be obtained by selection of high quality fluids. In the selection of hydraulic fluids, it is preferable to obtain fluids that are especially made for the particular application. Such fluids should be clean and of good quality.
Probably the greatest aid to trouble-shooting is knowing the system and how it operates. Every component motors, pumps, control and relief valves, fluid reservoir, oil filter and strainers has its purpose. The operating characteristics and purpose of each should be understood.
For example, knowing that a solenoid controlled directional valve can be manually actuated will save time in determining if there is a defective solenoid or a hydraulic pilot pressure problem. If the system works when the manual override is actuated, then the problem is electrical. Following the flow of electricity from the control switch to the solenoid valve should isolate the problem.
Know the correct operating pressures. Always set and check pressures with a gauge. If you do not know or are not sure of what the correct pressure setting should be, the following rule should be applied: the correct operating pressure is the lowest setting that will allow adequate performance of the system and still be below the maximum rating of the system. Excessively high pressures can damage the system.
The ability to recognize trouble indications in a specific system is usually acquired with experience. A few of the indicators are excessive heat or noise. Heat is generated by forcing oil through dirty or fine mesh filters and defective relief valves. Pump cavitation or slippage will also generate heat.
Excessive noise means wear, misalignment, cavitation or air in fluid. Contaminated fluid can cause relief valves to stick or chatter. These noises may be the result of dirty filters or fluid, high fluid viscosity, low reservoir level, loose intake lines or pump wear. On a vane type pump, when the ring starts to wear, the vanes start to skip, which sets up vibration and noise.
Safety and maintenance are so closely intertwined that, in most cases, one dictates the other. If you ensure maintenance and safety, along with operator education, you can have a trouble-free operation. A few minutes each day spent properly can prevent costly downtime and a possible accident in the future. The solution seems to involve eliminating the cause rather than treating the effect. And who can say that such an approach does not make sense?
Walter Geisler is vice-president of engineering with Screw Conveyor Corp., Hammond, Indiana, U.S., and Charles Cresap is the company's hydraulic hoists service manager. This article is based on their presentation to the 65th annual conference of the Grain Elevator and Processing Society in Cincinnati, Ohio, U.S.