CONTROL ENGINEERING

Made by :- Mechanical-2-B Roll no:-24,25 Mustafa Lokhandwala , Viken Sherdiwala

COMPONENTS OF PRESENTATION

Sealing Devices Filters and Strainers Regulators

LEAKAGE OF OILS Whenever there is a joint

mating surfaces may not match properly. Instead the surface irregularities of both the surface together form a small group through which the oil can leak out easily.

Seal is inserted between joints and pressure is applied by tightening of bolts.

Seal materials flows into irregularities of mating parts due to its plasticity and closes the flow path of oil and stops the leakage

CAUSE OF LEAKAGE

Irregularities in surface leading to improper mating of joints

Increase in clearances due to wear and tear of mating parts

Loosening of joints due shock and vibrations

Excessive operating pressures Fluid contamination Damaged or worn out seals

INTRODUCTION TO SEALING DEVICES

In any fluid transmission system the transmission of fluid between two points is possible only if the device applying pressure like a piston can apply pressure without any leakage of fluid.

In eighteenth  century Joseph  Brahmah  invented an effective piston seal, the cup packing. This led to development  of  the  hydraulic  press.

The packing was probably the most important invention in the development of hydraulics as a leading method of transmitting power. The development of machines to cut and shape closely fitted parts was also very important in the development of hydraulics.

CLASSIFICATION OF SEALS The packing materials are commonly referred to as seals or

sealing devices. The seals used in fluid power systems and components are divided into two general classes:-

(a) Static Seals (b)Dynamic Seals Static Seal :- The static seal is usually referred to as a gasket.

The function of a gasket is to provide a material that can flow into the surface irregularities of mating areas that require sealing. To do this, the gasket material must be under pressure. This requires that the joint be tightly bolted or otherwise held together.

Dynamic Seal :- The  dynamic  seal,  commonly  referred  to  as a packing, is used to provide a seal between two parts that move in relation to each other.

Many of the seals in fluid power systems prevent external leakage. These seals serve two purposes—to seal the fluid in the system and to keep foreign matter out of the system. Other seals simply prevent internal leakage within a system.

PROPERTIES OF SEALING MATERIALS Hardness Resistance to indentation, measured

using durometre. Softer materials are used for low

pressure applications while hard materials for high pressure applications.

Scale of hardness is given in ‘Shore A’ Scale from 0 to 100(degree). Shore A 70 scale is sufficient.

Permanent set It represents permanent distortion of

rubber after elongation (150% for 10 min at room temp).

Volume change – Swelling and Shrinkage Increase/decrease in size of elastomer as a result

of continuous contact with hydraulic medium. Swelling is desirable to some extent, as it causes

better sealing. But excessive swelling can cause friction.

Allowable is 20%for dynamic seals and 40-50% for static seals

Adhesion Susceptibility of rubber to stick to contact surface.

Aniline point It is the temperature at which fresh aniline may

react with oil.

Compression set Tendency of elastomer to loose it resilience. Compression set = loss in thickness * 100 Original thickness Permanent distortion of elastomer after

compression at a specified temperature for a period of time.

Final squeeze = Initial squeeze + Swell - Compression set

Squeeze Diametric compression of O ring between two

mating surface of Gland.

Tensile strength Tensile strength, elongation and tear

strenght affect the operation of seal due to physical contact and relative moment which tend to stretch, abrade, tear and wear of seal.

Ultimate elongation of seal is defined as maximum length to which an elastomeric seal may stretch before failure and seperation.

Ultimate elongation= separation length

* 100 free length

COMMONLY USED SEALING MATERIALS Cork Leather Metal Rubber Asbestos Elastomeric seal material

TYPES OF SEALS

T seals V-rings O-rings

FILTERS AND STRAINERS

A filter is a system of fine gauge meshes with depth. When fluid passes through these meshes or any other medium, the filter element will retain the insoluble impurities.

The particle size removed by filter is in microns, known as micron rating of a filter.

Strainers are similar to filters but without any depth. Their efficiency is less than the filters. Strainers are also called as coarse filters.

TYPES OF FILTERS

Based on filter material Metal elements (Porous type) Sintered

particles Mesh and cloth type media Edge type or Filter media Non metal element filters

TYPES OF FILTERS

Based on construction and flow Simplex filters Duplex filters Full-flow filters Proportional flow filters Filter/separator Indicating filters Inline or cone filters

Simplex filtersDuplex filters

Full Flow filter

Proportional flow filter

Indicating filterCone filter

LOCATION OF FILTER

Return line filter Intake filter or Suction Line filter Pressure filter

Inlet filter or Suction Line Filter

Pressure filterReturn line filter

REGULATORS

A pressure regulator is a normally-open valve that takes a high inlet pressure and converts it to a lower, pre-set downstream pressure.

To prevent constant opening and closing (chatter), the regulator is designed to open at a pressure somewhat lower than the closing pressure.

A regulator is open when it is directing fluid under pressure into the system. In the closed position the fluid in the part of system beyond the regulator is trapped at the desired pressure, and the fluid from the pump is bypassed into the return line and back to reservoir.

Why is it important to regulate Pressure in a Piping System?

Pressure is one of the most important aspects of ANY piping system. If pressure is too low, for example, the system is powerless. And if it is too high…

Just as high blood pressure damages the vital organs in your “piping system,”

overpressure affects filters, tools, sprayheads, instruments…any vital tool in a liquid piping system.

PURPOSE OF A PRESSURE REGULATOR…

Imagine having an employee who continuously monitors a single pressure gauge, and constantly tweaks a valve as downstream pressure rises or falls past a pre-determined point.

USES OF A PRESSURE REGULATOR:1. As a control element, to ensure that

downstream pressure does not exceed a set point.

2. As a safety device, to protect equipment from harmful overpressure.

3. Regulate to the correct pressure range so that a flow system or piece of equipment can operate safely and effectively.

HOW IT WORKS…

INLET OUTLET

A Set Screw

is used to set the desired pressure. It does this by controlling the force of non-wetted steel springs

The springs are attached to main shaft, and the force of the springs presses down, the main shaft

The valve seat

is part of the main shaft, and thus is held “open” by the force of the springs.

While the spring is holding the valve open and liquid is flowing through, a small tube near the valve outlet – called the “sensing orifice” – transmits downstream pressure into a chamber.

Because pressure is equal in all directions, the pressure in the chamber is identical to

downstream pressure.

SENSINGORIFICE

PRESSURECHAMBER

SENSINGORIFICE

PRESSURECHAMBER

VALVE OUTLET

ROLLING DIAPHRAGM

The key to this pressure chamber is a large Rolling Diaphragm. It rolls upward as pressure increases, and back down as pressure decreases…

In other words, it moves up and down in direct response to changes in downstream pressure.

SENSINGORIFICE

PRESSURECHAMBER

VALVE OUTLET

ROLLING DIAPHRAGM

The Rolling Diaphragm is attached to the Main Shaft that we mentioned earlier – which as you recall, is held down by spring force, which in turn holds the valve open.

SPRINGFORCE

M AIN SHAFT

VALVE IS HELD OPEN

But when pressure at the outlet increases…

…as downstream pressure increases, the force on the rolling diaphragm increases, in direct opposition to the spring force...

When downstream pressure exceeds the spring force, the rolling diaphragm overpowers the springs.

This compresses the springs and forces up the main shaft...

The valve seat, as part of the main shaft, closes against the main internal orifice, preventing additional pressure downstream.

It will remain closed as long as downstream pressure exceeds the set point, as determined by the set screw controlling the force on the springs.

When downstream pressure falls below the set point, the valve begins to re-open as the springs again force the main shaft down. Flow resumes.

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• Most pressure regulators impede flow while sensing pressure. The sensing orifice and pressure sensing chamber in a regulator are not in the flow path – flow is unrestricted and much higher than competitive designs.

• Large sensing area of the rolling diaphragm provides smoother, more accurate control.

ADVANTAGES OF PRESSURE REGULATORS

• U-cups used in place of o-rings provide smooth, non-sticking movement of the main shaft.

• Greater accuracy & repeatability achieved via springs matched to the pressure range of the application.

• Overall design – large flow path, large sensing area, more sensitive springs – all combine to provide the best performing pressure regulators since 1967.

• No wetted metals. All-plastic wetted designs are essential for corrosive and ultra-pure applications.

ADVANTAGES OF PRESSURE REGULATORS

Thank you