Hydraulic Intensifier

1. INTRODUCTION

A hydraulic intensifier is a device which is used to increase the intensity of pressure of any hydraulic fluid or water, with the help of the hydraulic energy available from a huge quantity of water or hydraulic fluid at a low pressure. Know about the components and construction of intensifiers. A hydraulic intensifier is a hydraulic machine for transforming hydraulic power at low pressure into a reduced volume at higher pressure. A hydraulic intensifier is a device which is used to increase the intensity of pressure of any hydraulic fluid or water, with the help of the hydraulic energy available from a huge quantity of water or hydraulic fluid at a low pressure. These devices are very important in the case of hydraulic machines, mainly hydraulic presses, which require water or hydraulic fluid at very high pressure which cannot be obtained from the main supply directly. In most of the hydraulic machinery used, the usual pressure of 80 to 100-psi may not be sufficient to operate certain spool valves and other mechanisms. To cater to the need for a high pressure requirement for a comparatively short period of time, pumps and accessories are definitely not the solution. But the substitute can be hydraulic intensifiers which can increase the pressure from 100 psi to 40,000 psi, using small volumes of fluid. There are different types based on the medium of hydraulic fluids used and the number of strokes used to intensify to the desired pressure. They are single-stroke, differential cylinder intensifiers, oil-oil intensifiers, air-air intensifiers, and oil-air intensifiers. Recent developments are so vast that huge pressures are achieved by using combinations of the above types. An intensifier heightens the intensity of the meaning of an item. A hydraulic intensifier is a hydraulic machine for transforming hydraulic power at low pressure into a reduced volume at higher pressure. It increases the intensity of pressure of the liquid by utilizing the energy of a larger quantity of liquid at low pressure. Such a machine is constructed mechanically by connecting two pistons, each working in a separate cylinder of different diameter. This concept is developed from Pascal’s law for incompressible fluid. If the diameters of the pistons are different, the hydraulic pressure in each cylinder will vary with the area ratio of the pistons, the smaller piston giving rise to higher pressure intensity than the larger piston pressure intensity. The increase in the intensity of pressure is generally required when the liquid supplied by the pump does not possess the required intensity of pressure. The hydraulic intensifier is very important in the case of hydraulic machines, mainly hydraulic presses, which require water or hydraulic fluid at a very high pressure which cannot be obtained from the main supply directly. High pressure metal hydro-forming requires 20,000 psi or 1379 bar [3]. Definitely this pressure will require a massive construction of pump. But if there is a HPI, it is possible to raise the pressure by using a reasonable size of pump. A machine which has come into general use very rapidly in the last few years is the high-speed forging press for casting and forming heavy and complicated shapes. The next broad step after the direct pump-driven press was the hydraulic intensifier which made it possible to raise the pressure which cannot be achieved directly by pumping action. To press two metals sheet adjacently and to lifting heavy load, as for example, bridge slab, it requires a device which is capable of heavy load carrying capacity and smooth operation. Again, it is hydraulic jack which possesses the capabilities of smooth operation and heavy load carrying behavior. But for its proper functioning it is necessary to supply the compressed fluid at high pressure and this can be done by using a HPI. Hydraulic intensifier is used in constructing water cutting jet machine. It is also used in mining and construction firms. The objectives of the present work is to design and construct a automatic controlled reciprocating HPI which can maximize pressure 6.25 times the input pressure range of maximum 5 bar. In existing rotary type HPI critical intensification ratio is 2.5 and its efficiency is 45%.

2. THEORETICAL STUDY

Hydraulic Pressure Intensifier is a mechanical device which is used for increasing the intensity of pressure of the liquid by utilizing the larger quantity of liquid at low pressure. Often hydraulic machines such as press, etc., require liquid at high pressure which may not be directly available from a pump. It can, however, be provided by introducing an intensifier between the pump and machine. It consists of several kinds of mechanical and electrical equipment.

2.1 Classification

Basically there are only two types of hydraulic intensifier namely single action and double action intensifier. These two principal types of hydraulic intensifier have been modified in so many ways as per requirements of industry. Some of them are described as follows: Classification based on body construction of Hydraulic intensifier:

2.1.1 Tie-Rod Construction

This type of construction is most widely used in industry. ISI standard also generally refers to one of this type of construction. As all the components are only machined and assembled together and not welded. Hence planning manufacturing, quality control assembly and maintenance are more convenient than other types of construction. As long as tie-rods are used to hold the entire components together, special care is required to tighten them and safe-guard against loosening in operation.

2.1.2 Threaded Construction

This construction is similar to tie-rod construction, but more compact, stronger, and requires more accuracy and care in manufacturing and quality control. In this design, both ends are assembled with cylinder-tube by threading, as shown in following design. These are used for medium to heavy-duty operation, and widely used in earth-moving purpose respectively.

2.1.3 Bolted Construction

This type of construction involves welding of flanges to cylinder tube, and bolting of end cover to the welded flange. Similar to tie rod construction these are also designed and manufactured as standard hydraulic component and widely used in industry.

2.1.4 One Piece-Welded Cylinder

Similar to shock absorber, in this design the end-covers and cylinder tube are welded together. These are economical but cannot be repaired.

These are used for low pressure agriculture machinery application. Figure 4 shows One Piece-Welded HPI.

2.1.5 Custom Build HPI

In this type of cylinder, various type of construction is mixed together to suit the requirement. One of the most widely used combinations is welded cap-end cover, bolted head-end cover with front tube flange mounting. In case of high capacity cylinder when it is steel cast or machined from solid steel forging, then end cover and front flange may be integral part of cylinder tube. Cylinder with this type of construction is widely used in hydraulic press.

2.2 Main Parts

A hydraulic pressure intensifier consists of several kinds of mechanical and electrical components. There are two main parts in the hydraulic intensifiers to be noted. These are Piston and Cylinder.

2.3 Working Principle of HPI

The working principle of HPI is described below:

1.     Oil is forced into the right half of the hydraulic cylinder.
2. The piston-plunger assembly moves to the left. Oil is displaced out of the left half of the hydraulic cylinder and the water in the left high pressure cylinder is pressurized.
3.  The plunger moves to the left.
4.   Once pressure has begun to build, the high pressure water is forced out of the intensifier through the center of the check valve.
5.  While the piston-plunger assembly is moving to the left, it is also allowing fresh water to flow into the right high pressure cylinder through the inlet holes of the check valve.
6.   When the plunger-piston assembly has reached the end of its stroke to the left, the right high pressure cylinder is now full of water.
7.    The directional control valve receives a signal via a proximity sensor near the piston to reverse the flow of hydraulic oil. Oil is now forced into the left half of the hydraulic cylinder and the piston moves to the right.
8.   Oil is displaced out of the right half of the hydraulic cylinder while the water in the right high pressure cylinder is pressurized by the right plunger. Such a machine may be constructed by mechanically connecting two pistons, each working in a separate cylinder of a different diameter. As the pistons are mechanically linked, their force and stroke length are the same. If the diameters are different, the hydraulic pressure in each cylinder will vary in the same ratio as their areas: the smaller piston giving rise to a higher pressure. As the pressure is inversely proportional to the area, it will be inversely proportional to the square of the diameter.

3. OPERATION

The working volume of the intensifier is limited by the stroke of the piston. This in turn limits the amount of work that may be done by one stroke of the intensifier. These are not reciprocating machines (i.e. continually running multi-stroke machines) and so their entire work must be carried out by a single stroke. This limits their usefulness somewhat, to machines that can accomplish their task within a single stroke. They are often used where a powerful hydraulic jack is required, but there is insufficient space to fit the cylinder size that would normally be required, for the lifting force necessary and with the available system pressure. Using an intensifier, mounted outside the jack, allows a higher pressure to be obtained and thus a smaller cylinder used for the same lift force. Intensifiers are also used as part of machines such as hydraulic presses, where a higher pressure is required and a suitable supply is already available.

Some small intensifiers have been constructed with a stepped piston. This is a double-ended piston, of two different diameters, each end working in a different cylinder. This construction is simple and compact, requiring an overall length little more than twice the stroke. It is also still necessary to provide two seals, one for each piston, and to vent the area between them. A leak of pressure into the volume between the pistons would transform the machine into an effective single piston with equal area on each side, thus defeating the intensifier effect. A mechanically compact and popular form of intensifier is the concentric cylinder form, as illustrated. In this design, one piston and cylinder are reversed: instead of the large diameter piston driving a smaller piston, it instead drives a smaller moving cylinder that fits over a fixed piston. This design is compact, and again may be made in little over twice the stroke.

It has the great advantage though that there is no "piston rod" and the effective distance between the two pistons is short, thus permitting a much lighter construction without risk of bending or jamming. In the example illustrated, the two pistons are approximately 1:2 ratio in diameter, giving a 1:4 increase in pressure. Note that it is the diameter of the effective piston, i.e. the seal diameter that matters. The cylinders here are relieved beyond the seal and are of greater diameter, for easy running. Although the moving cylinder's bore is around ¾ of the outer diameter, not ½, it is its seal diameter that matters, not its internal clearance bore.

The celebrated mechanical engineer Harry Ricardo began his career by working in his grandfather, Alexander Rendel's, civil engineering practice. At the time they were involved in the construction of bridges in India, which required hydraulic lifting, hoisting and riveting equipment. As the existing transport infrastructure was poor, all plant used on site needed to be lightweight and easily portable. Machines also needed to be connected to their hydraulic power source by flexible tubing, which limited their working pressure to around 500 psi. At this time, modern shipyard equipment was using pressures of up to 2000 psi. This high-pressure equipment was smaller and lighter than the bulkier low-pressure variety, a desirable feature for this construction work. Ricardo's innovation was to specify the use of portable hydraulic intensifiers for these tools, permitting the use of the improved high-pressure form, even where their supply was at low-pressure, through flexible hose. These intensifiers were so successful that eventually several hundred were supplied and used.