How Does a Hydraulic Pump Work

The advantage of using a hydraulic machine is that more force and torque can be generated with relatively smaller sized machines without requiring a gear system. An important component of a hydraulic machine is the hydraulic pump. The supply of fluids like oil and water to the various components of the machine is accomplished by using hydraulic pumps. Their mechanism is based on the displacement of the fluid volume against a resistant load or pressure.

Hydraulic Machinery

The machines that make use of fluid power to carry out the necessary function or to do work in general are called hydraulic machinery. In these machines, a fluid having high velocity is distributed to the hydraulic motors and hydraulic cylinders through tubes of small diameters. This fluid is known as the hydraulic fluid, and it can be oil, water, gas, etc. Control on the fluid is exercised with the help of control valves that are controlled automatically. A hydraulic pump is an important component of the working process of a hydraulic motor.

Basic Concept of Hydraulic Pumps

Basically, pumps are meant to impart energy to anything flowing through them. They transfer the fluid from a low potential to a high potential as in heat pumps. When a fluid enters a hydraulic pump, it has some velocity of its own. Now, with the help of an external energy source the pump boosts the velocity of the fluid. The rotating parts inside the pump carry out processes like confining the fluid in a certain volume and displacing it to increase its energy. It should be noted that hydraulic pumps do not generate any pressure, and they simply render the fluid with more velocity.

Positive Displacement Pump Principle

In general, pumps can be classified as positive displacement pumps and non-positive displacement pumps. Hydraulic systems mostly make use of positive displacement pumps. As the article is on the processing of hydraulic pumps, working of the positive displacement pumps will be discussed further. Positive displacement implies displacing a fixed quantity of something. In the case of hydraulic pumps fluids, a positive displacement pump has an increasing opening on the suction side of the pump and a decreasing outlet on the discharge side. When liquid flows in to the pump, it is forced out with greater velocity as the discharge side outlet is decreasing in size. Positive displacement pumps can further be classified under subcategories according to the motion pattern of the enclosed volume forming parts. Operating a positive displacement pump against a closed valve on the discharge side should be avoided, and a safety valve on the discharge side of this pump is mandatory.

Types of Positive Displacement Pumps

Reciprocating Pumps
This is the most basic type of positive displacement pump. In a reciprocating positive displacement pump, the moving part that is the piston, has a reciprocating motion. The discharge in this pump is pulsating and varies only when the speed of the pump is changed. The reason being that the intake is in constant volumes. Reciprocating pumps are often implemented for sludge and slurry. The two types of reciprocating pumps are plunger pumps and diaphragm pumps.

Metering Pumps
These pumps are used for precisely controlling very low flow rates. Flow rates are generally less than ½ gallon per minute. They are usually used to control additives to the main flow stream. These pumps are also called controlled volume pumps. Metering pumps have types such as diaphragm and packed plunger. Unlike the reciprocating positive displacement pumps, the metering pumps are meant to be used for clean fluids and impurities that can clog the valves of the pump.

Rotary Pumps
The rotary positive displacement hydraulic pumps come in the following types - the gear pumps, lobe pumps, vane pumps, progressive cavity pumps, peripheral pumps, and screw pumps. In these pumps, rotary motion carries the liquid from the pump inlet to the pump outlet. The fluid gets trapped in the closed casing of the rotary pump and is discharged in a smooth flow.

The basic information on the mechanism of hydraulic pumps, and their various types, has been provided above to give you an introduction to the subject. Hydraulics in itself, is a vast field and various books are available that will provide you more in depth information on the it.

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Rebuild a Hydraulic Cylinder

Hydraulic systems are widely used in agriculture, construction and manufacturing industry. Bulldozers, cranes, tractors, elevators and all such heavy machines use hydraulics. Hydraulic hybrid vehicles are some of the newest developments in this field of technology. Hydraulics is an applied science, which exploits the mechanical properties of fluids to build hydraulic systems that can perform heavy duty mechanical jobs with precision. Hydraulic systems offer power with precise control and versatility. At the core of every hydraulic system is the hydraulic cylinder. It is the central component on which all hydraulic systems are dependent. Therefore, one must learn rebuilding these cylinders, as it saves money and valuable time.

Construction and Working

Any hydraulic system is made of two parts; the hydraulic pump that generates the pressure and the hydraulic cylinder that delivers the mechanical action in response to pressure. The cylinder is a barrel fitted with a piston, which fluidly moves back and forth. The cylinder barrel is of course sealed from both ends.

The piston divides the barrel body into two parts; the rod end, which is the side from where piston enters the barrel body and the other side, which is capped, called the cap end. The piston is driven back and forth, by the hydraulic fluid, which is mostly oil, introduced by the hydraulic pump. The piston has sliding rings and seals, which prevent the leakage of fluid from one part of the piston compartment, to the other part. The piston is connected with appropriate mounting arrangement. It conveys piston motion to appropriate moving part of the machine, which carries the load.

The idea behind every hydraulic system working is simple. The pressure applied at one point is conveyed to other point by the use of an incompressible fluid which is usually oil. So when the pump pushes oil into the piston chamber, from the cap side, the piston is lifted up. When oil is sucked back by the hydraulic pump from the chamber, the piston gets pushed down. This is how a hydraulic system works by conveying force through an incompressible fluid. By using pistons of different surface areas, force multiplication can be achieved. A heavier load can be lifted up by relatively lesser force, using this principle!

Repair Tips

Here are some common problems that can break a cylinder or cause its malfunctioning. I will outline the possible solutions that can help you rebuild or repair your cylinder. Read instruction manuals for the machine supplied by the manufacturers carefully, before going ahead.

Problem 1: The cylinder is cracked or piston rod is bent

Solution: If on observation, you see the cylinder rod is bent or the cylinder barrel is cracked, there is pretty much nothing you can do. It's time to replace the cylinder. Forging a new barrel or straightening the piston rod is beyond your capacity. So if this is the case, repairing the cylinder is not possible. In such a case, only a specialized repair shop can rebuild the cylinder for you, as a customized new shaft may need to be forged and the cylinder bore may need to be honed.

Problem 2: The seal is broken

Solution: If the shaft seal is broken, the pressurizing fluid leaks and loses pressure, impairing working of the cylinder. It can be replaced. However, an opening of the entire cylinder assembly is necessary. Let us see how we can go about it. Obtain a diagram of the cylinder if possible, as it will help you in reassembly. These diagrams can be had from the equipment manufacturers and you can also carry a printout. You can order a standard repair kit for your cylinder which is supplied by the manufacturing company. It includes spare cylinders, spare seals, O-rings and other spare parts according to the number and type of cylinders in your machine.

The assembly of the cylinder varies with machine type. Locate the seal position first. Mostly, you will find it around the shaft on one end. The shaft entry end can be accessed by unscrewing the lid from that side. You may need to unscrew the bolts, to remove the cover. Then loosen the pipes or valves that transmit the hydraulic fluid into the chambers which will release pressure. This will enable you to remove the shaft which otherwise cannot be removed due to hydraulic pressure. Handle the shaft carefully and take care that you do not scratch it. Detach the piston from the shaft and replace the seal with the spare one from the repair kit. Make sure that the seal is aligned rightly. Oil all parts after fitting and reassemble everything in exactly reverse order.

Problem 3: Piston Rings are damaged

Solution:If the piston rings are damaged, then they can be replaced too, by the same disassembling procedure, as for the above problem. The piston rings need to be removed and replaced very carefully. Oil the rings and cylinder assembly, before putting back everything together.

If you have a multiple cylinder arrangement, things are more complicated. It is better to consult a qualified technician before going ahead. Always remember one rule, while you are solving mechanical problems, do not proceed without a reason to take a particular action. Also, study the assembly and causative framework of the machine before going for repair. This repair can be a good learning experience for anyone who loves machine design.

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Fuel control dial

Function
• The fuel control dial is installed under the monitor
panel, and a potentiometer is installed under the
knob. The potentiometer shaft is turned by turning
the knob.

• As the potentiometer shaft is turned, the resistance
of the variable resistor in the potentiometer
changes and a throttle signal is sent to the
engine throttle and pump controller.
The hatched area in the graph shown at right is
the abnormality detection area.

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How do Hydraulics Work

In today's world, we can see that many of the machines used for industrial purposes make use of hydraulics. The use of hydraulics has streamlined the working of heavy machines. Arduous tasks such as lifting (cranes), stone crushing (diggers), etc. have become easier.

Hydraulics is a subject in engineering which deals with the study of mechanical properties of fluids. Pressurized liquids are used in the generation of power, its control and in its transmission. Various concepts such as fluidics, dam design, pipe flow and fluid control circuitry are studied in hydraulics.

Working of Hydraulics
The idea behind the working of hydraulics is very simple. Mechanical force applied at one point is carried to the desired point by means of a fluid (incompressible). Different types of hydraulic motors and cylinders make use of this fluid power in the functioning of machines. Tubes and hoses direct the flow of fluids while control valves regulate their flow. One may find several applications of hydraulics in the form of car brakes, garage jacks, motorboat steering, cranes and garbage trucks among others.

To understand why fluids hold so much importance in the functioning of hydraulic machinery, let us try to understand the concept of hydraulics by means of the example of water pistol. In water pistol, the spout or opening, through which the water squirts, is narrow, while the place at which force is applied (trigger) is comparatively wider. When our finger applies force by means of the trigger, water is pushed towards the narrow spout. Since, fluids are incompressible, the resulting speed with which water comes out of the opening is greater as compared to the speed with which trigger is pressed.

In different machines that work on the principle of hydraulics, the course of action which takes place, is exactly opposite/reverse to what is illustrated in the above example. Now, imagine that water is forced through a narrow spout at high speed, the force generated at the other (wider) end would be sufficient enough to carry out a mechanical action. The big machines like cranes, diggers, etc. make use of fluid tubes and rams. The drivers of these machines (vehicles) operate the process of forcing in fluids through narrow tubes; which in turn push the rams into action. The functioning of hydraulic machines is based on this simple concept. It helps us in understanding how hydraulics are used and the methodology behind various applications in industrial hydraulics.

Hydraulic Engineering
It is one of the branches of construction engineering which deals with conveyance of liquids and primarily, water. The activity of designing dams, bridges, canals, channels, levees, etc. comes under this branch of engineering. Maintenance of aqueducts, an activity which comes under the purview of hydraulic engineering was carried out during the Roman Empire. The science of hydraulic engineering is related to geotechnical and transportation engineering, since hydraulic engineers have to construct water collection networks, water distribution networks, undertake storm water management and also deal with sediment transportation.

Pneumatics and Hydraulics
The main difference between hydraulics and pneumatics is that liquids are used in the former, while the later makes use of gases in its various applications. Gases can be compressed, while fluids are incompressible. The working pressure in hydraulics is much greater in comparison to that in pneumatics.

The above article helps us in understanding how do hydraulics work through easy to understand examples and some basic information related to the core concept. There is a lot to say and understand about the interesting subject of hydraulics.

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