Pressure Intensifiers

 Pressure intensifiers, also known as pressure boosters, are used to compress the liquid in a hydraulic system to a value above the pump discharge pressure.

PRESSURE INTENSIFIERS

INTENSIFIERS

1. What are Pressure Intensifiers ?

• Pressure intensifiers, also known as pressure boosters, are used to compress the liquid in a hydraulic system to a value above the pump discharge pressure.

• In other words, a hydraulic intensifier is a device which converts a large-volume, low- pressure fluid supply into a proportionately small-volume, high-pressure fluid outlet.

• The intensifier is usually located in between the pump and the machine (e.g., press, crane, lift) that needs high pressure liquid for its operation.

• The action of the intensifier is similar to that of a step-up electrical transformer.

• Applications: It finds its application at places where a liquid of very high pressure is to be developed from available low pressure. Typical applications include hydraulic presses, riveting machines, and spot-welders.

2. Construction and Working

The construction and operation of a typical pressure intensifier is illustrated in Fig.9.18.

As shown in Fig.9.18, the unit consists of two pistons-low pressure and high pressure- having a common piston rod. The larger, piston is exposed to pressure from a low-pressure pump. The low-pressure fluid (oil) is introduced to the larger piston side and thus it forces the piston to move. Neglecting losses due to friction, the smaller end of the piston exerts the same force on the fluid in the intensifier chamber or smaller cylinder.

3. Intensifier Ratio

It may be noted that the increase in pressure is directly proportional to the difference in areas of the two sizes of pistons.

Let

Po = Pressure exerted on larger or 'operating' end of the piston,

Pi  = Pressure exerted by smaller or 'intensifying' end of the piston,

A。= Area of the larger or 'operating' end of the piston, and

Ai = Area of the smaller or 'intensifying' end of the piston.

Since force load acting on the two pistons is same, we get 

Po × A。 = Pi × Ai

4. Graphic Symbol

Fig.9.19(a) and (b) show the symbolic representation of a pressure intensifier having single- and double-acting piston respectively.

5. Advantages

Some of the important advantages of employing the pressure booster are as follows:

1. In circuits which require low-volume high-pressure flow over short period, the pressure intensifier eliminates the need of expensive, high-pressure pumps.

2. This unit is more compact and simple than adding another power unit for high-pressure cycling.

3. A low power input can be used to maintain a high pressure for a period of time.

4. Because of the seal between the high- and low-pressure chambers, the intensifier can be operated with a liquid different from that used in the high-pressure part of the circuit.

5. Since the high-pressure is produced with small volume of oil, the heat generated is minimum.

6. It automatically connects' with the circuit when high-pressure is required and disconnects when the demand is satisfied.

7. Its kW power requirements remain constant.

6. Ranges

The pressure intensifiers are available with pressure ratio ranging upto 50 to 1, developing pressures to 350 bar, and flow rate to 0.5 Lps.

7. Applications

• Intensifiers find most useful applications where the output pressures requires are much higher than are obtainable from a pump.

• Typical applications include punching presses, riveting machines, spot-welders, and in many high-pressure testing machines such as tubing fixtures for testing bursting pressures and high pressure holding fixtures.

Note 

The circuit and operation of important pressure tensifier circuits are presented in Chapter 9, Section 9.13.

Example 9.8

A hydraulic fluid at 2 Lps and 75 bar enters the low-pressure inlet of a 5 : 1 pressure booster. Find the discharge pressure and flow rate.

Given Data: 

Solution: 

Example 9.9 

A hydraulic intensifier gets the low pressure liquid at a pressure of 50 bar and delivers it to a machine at a pressure of 150 bar. If the intensifier has a capacity of 0.025 m3 and stroke 1.25 m, calculate the diameters of the intensifier chamber and the larger cylinder tő be used for this intensifier.

Given Data: 

Po = 50 bar; Pi = 150 bar; Capacity = 0.025 m3 Stroke = 1.25 m. ;

Solution: 

(i) Diameter of the intensifier chamber (Di) : 

We know that,

Capacity of intensifier = Area of intensifier chamber (Ai) × Stroke length

Or 0.025 = Ai × 1.25

Or Ai = 0.02 m2

(ii) Diameter of the larger cylinder (Do) :

For the pressure intensifier, we know that

Example 9.10

Design a puħching press with five working stations operated by five single-acting cylinders connected to an intensifier. The cylinders require 20 mm travel and used to punch 20 mm diameter holes on sheet metals of 5 mm thick of mild steel whose strength is 360 MPa. Determine the oil pressure of the hydraulic system and length of the intensifying cylinder if the load piston area is 20000 mm2, ram piston area and small piston area of the intensifier are 15000 mm2 and 900 mm2 respectively. 

Given Data: 

Diameter of hole to be punched, D = 20 mm; Stroke length required, L = 20 mm; Thickness of the sheet material, t = 5 mm; Shear stress of the sheet material = 360 MPa = 360 × 106 N/m2.

Solution: The given punching press circuit can be drawn as shown in Fig.9.20.

(i) To find the oil pressure of the hydraulic system:

This pressure is to be delivered at the outlet of the intensifier.

Therefore, the pressure required at the inlet of the intensifier from the pump (P) is given by

(ii) To determine the stroke of the intensifier to have a punching stroke of 20 mm at all five load cylinders:

Let L1 = Length of intensifier stroke required to supply oil to 5 load cylinders.

Volume of fluid required at the punching end, Qp = 5 × Area of load piston × Stroke

= 5 × (20000 × 10-6) × (20 × 10−3) 

= 0.002 m3

Volume of the intensifier Qp = Area of outlet piston × L1

= (900 × 10−6) × L1