This document provides information on mechanical seals used in hydraulic systems. It discusses how centrifugal pumps work and the need for seals to prevent leakage of pressurized liquid around the pump shaft. Mechanical seals were developed to improve on common packing seals, reducing leakage and wear. The document covers types of leakage, functions of seals, classifications of seals based on design and materials, and basics of fluid power symbols.

1. ACCESSORIES USED INACCESSORIES USED IN
HYDRAULIC SYSTEMSHYDRAULIC SYSTEMS
MECHANICAL SEALSMECHANICAL SEALS

2. INTRODUCTIONINTRODUCTION
• Hydraulic systems are associated with a
major problem – Leakage.
• This causes to reduce efficiency and
increase the power losses.
• Mechanical seals are means of controlling
the leakage process where other means
are less capable of performing the tasks.

3. CENTRIFUGAL PUMPSCENTRIFUGAL PUMPS
• A centrifugal pump is simply a
shaft, suspended on bearings with
an impeller attached to one end.
The impeller is encased in a
housing that is filled with a liquid.
As the shaft is rotated, centrifugal
force expels the liquid out through
an orifice, where it is typically
piped into a process or another
collection point. As the expelled
liquid exits the case, additional
liquid is added to the case so that a
flow develops. That is basically
how a centrifugal pump works.

4. PUMP SHAFT
BEARINGSIMPELLER

5. AS THE PUMP SHAFT ROTATES
A LIQUID IS SUPPLIED TO
THE PUMP “SUCTION”
CENTRIFUGAL FORCE EXPELS THE
LIQUID OUT FROM THE IMPELLER

6. • The force of the expelled liquid creates pressure. This liquid
under pressure will seek areas of lower pressure. This is a
known physical principle of hydraulics. Some form of seal
must be applied to keep liquid from leaking around the shaft at
the point where it enters the case to drive the impeller. This is
where our mechanical seal comes into play.
• Take a look at the same pump again. Can you see the
mechanical seal behind the impeller?

8. SEALING THE LIQUIDSEALING THE LIQUID
• Mechanical seals were originally designed to lend a
greater sealing capability than could be achieved using
common packing.
• Before the advent of mechanical seals, pump users relied
primarily on “rope” or braided style packing to achieve a
“seal” around the shaft. A series of pieces or “rings” were
installed into the pump “stuffing box” and they were
compressed tightly so that they created a difficult leak
path for the liquid to negotiate in order to leak to
atmosphere.

10. SEALING THE LIQUIDSEALING THE LIQUID
• Early packing styles did not seal very well. In fact, until
recently, braided packing styles required varying amounts
of leakage for lubrication. If leakage was not permitted to
occur, the packing would literally “burn up” and often
cause severe damage to the pump shaft. Even with
adequate leakage for lubrication, pump shaft wear was a
commonly expected occurrence and as the shaft wore it
would in turn, cause poor shaft packing life.
• As leakage becomes more excessive, the gland is
tightened to reduce leakage.

16. SEALING THE LIQUIDSEALING THE LIQUID
• With the introduction of mechanical seals, this leakage
could be controlled to a much greater degree.
• Let’s look at the same pump with a mechanical seal
installed. Note that the seal shown is an RS-1 with O-
Ring type stationary and a set screw collar.

19. SEALING THE LIQUIDSEALING THE LIQUID
• You have probably taken notice of the illustration showing
minor leakage to atmosphere. It is appropriate to point
out at this time…

20. ALL
MECHANICAL SEALS
LEAK
.
LESSON NUMBER ONELESSON NUMBER ONE

21. Types of Leakages
• Internal Leakage:
This occurs in hydraulic built with operating
clearance.
Moving path needs to be lubricated and leakage
path may be solely designed for that purpose.
Internal leakage does not cause loss of fluid as it
returns to the reservoir.
This leakage increases clearance and causes wear.

22. Types of Leakage
• External Leakage:
Loss of fluid occurs
Safety hazard
Caused due to improper assembly of pipe fittings
Over tightened fittings may become damaged and
vibration can cause leakages.

23. Functions
• Prevent leakages both internally as well as
externally
• Prevent dust and other particle from
entering into the system
• Maintain pressure
• Enhance service life and reliability of the
hydraulic system.

24. Classification
1. According to the method of sealing:
• Positive Sealing: a seal which prevents
even a minute amount of oil from getting
past, it doesn’t allow any liquid to flow.
• Non-positive Sealing: these are assembled
between the mating parts that move
relative to one another. Hence they are
subject to wear.

25. 2. According to the relative motion
occurring between the seals and other
parts:
•Static Seals:
Static seals are used to prevent two surface
having no relative motion between them. Eg:
Gaskets
•Dynamic Seals:
It is used when leakage of oil between two
moving parts is to be stopped. Eg: Rings,
Stuffing box.

26. • According to the geometrical cross-
section:
O Ring Seal:
O ring can be used for static as well as
dynamic conditions
It gives effective sealing over a wide range of
pressure.
Use of backup washers is necessary in this
type of seal

28. • V type seals
V rings and U rings are compression type
seals used in all types of reciprocating
motion applications.
Piston rods and Piston seals in press rank,
jacks, seals on plunger and piston in
reciprocating pumps.

29. • T ring seals
• Piston rings
• Wiper rings and Scrapper rings:
They are used to wipe out foreign materials
like dirt abrasive material or contaminants
from the piston rods. To extend the life of
rod seals dirt extrusion is necessary.

30. 4. According to the type of seal material
used:
These seals are made from variety of natural
and synthetic materials. Mostly plastic and
synthetic rubber is used.
•Neoprene (Chloroprene)
•Buna-N
•Silicone (Teflon)
•Tetrafluoroethylene
•Viton

31. Classification of Fluid Power
Lines
• Pipe (Rigid)
• Tubes (Semi-Rigid)
• Hoses (Flexible)

32. Schedule of Pipes & Schedule
Number
Classification of pipes is done based on their
wall thickness viz.
-Standard Pipes
-Extra Strong Pipes
-Double Extra Strong Pipes
But as per new classification, the wall
thickness is expressed as Schedule number
(ANSI)

33. Schedule Number
• Higher the wall thickness of pipes used, the
ID will determine the bursting pressure of a
line i.e for a given ID, greater the wall
thickness, greater will be the bursting
pressure.
• Standard- Schedule 40
• Extra Strong- Schedule 80
• Double Extra Heavy – Schedule 160

34. Basics of ISO Symbols
Purpose:
1.The purpose of this standard is to provide a system
of fluid power graphic symbols for industrial and
educational purpose
2.The purpose of this standard is to simplify design,
fabrication, analysis and service of fluid power
circuits.
3.The purpose is to promote universal understanding
and to provide symbols which are internationally
recognized.

35. Symbols
NAME SYMBOL MEANING
PNEUMATIC TO ILLUSTRATE
THE FLOW
DIRECTION
HYDRAULIC
CONNECTED SYSTEM IS
CONNECTED
DISCONNECT-
ED
SYSTEM IS
DISCONNECTED

36. DIAMOND SYMBOLS

37. Basic Symbols
Line Working line, pilot supply,
return, electrical
Chain Enclosure of two or more
functions in one unit
Dashed Pilot control, bleed, filter
Line Electrical line
1
2
3
12 10

38. Valve symbol structure
• The function of a valve is given by a pair of
numerals separated by a stroke, e.g. 3/2..
• The first numeral indicates the number of
main ports. These are inlets, outlets and
exhausts but excludes signal ports and
external pilot feeds.
• The second numeral indicates the number of
states the valve can achieve.

39. Valve symbol structure
• A 3/2 valve therefore has 3 ports (normally
these are inlet, outlet and exhaust) and 2
states (the normal state and the operated
state)
• The boxes are two pictures of the same
valve
normal
operated