Maintenance Awareness

Fluid Systems

Orlando Moreno+1 770.354.3072 omoreno@hotmail.co

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Manufacturing Fundamentals

Contrast the two types of fluid power systems.

List the three fluid power laws. Describe different types of pumps Present the factors that affect fluid power

system efficiency.3/61

Learning Objectives

What is Fluid Power?

Energy transmitted by pressurizing and controlling a contained fluid.

Transports power from one location to another.

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Types of Fluid Power Systems

Pneumatic Systems Air, CO2 and other gases

Hydraulic Systems Oil or hydraulic fluids (non-

compressable)

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W earband R od Bearing

P iston Seal

Static Seals

R od W iper

R od Seal

A ir B leed

R od C artridge

P iston

Figure 7-6 Typica l cylinder construction

CO PYR IG HT (2001) EATO N CO RPO R ATIO NC

Static Seals

A ir B leed

Seals Piston seal

Cast iron piston rings Prevents fluid from internally bypassing the piston Permits slow drifting with the control valve closed

Rod seal Rubber-like materials Sealing of moving surfaces

Prevents external fluid leakage along the rod Rod wiper or scraper

Keeps foreign material from entering the cylinder and system Maintenance is very important

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Cylinders

Basic Pneumatic System

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Directional Control Valve

Cylinder

Basic Hydraulic System

PPressure

Pump

Reservoir

Hydraulic Power Unit (HPU)

ReservoirPumpFilterControl Valve

Filter

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Two Types of Loop Fluid Power Systems

Closed loop system Hydraulic fluid is circulated in a

pressurized system Open loop system

Pneumatic systems vent to the atmosphere

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Parts of a Basic Hydraulic System

Reservoir Pump - power source Filter Directional control device Cylinder Stainless Steel Tubing

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Wisc on line – flowWisc on line – pumps

Three Laws of Fluid Power Systems

Pascal’s LawBoyle’s LawCharles' Law

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Pascal’s Law

Pressure is the same throughout the entire vessel.

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Pascal’s Law (Cont’d.)

Pressure applied on a confined fluid is transmitted undiminished in all directions, acts with equal force on equal areas, and at right angles to them.

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1. The bottle is filledwith liquid, which isnot compressible

2. A 10 lb. force is appliedto the stopper with a surface area of one square inch

3. This results in 10 lb of force on every square inch of surface area in the container

4. If the bottom has an area of 20 sq. in. and each square inch is pushed on by 10lbs. of force, the entire bottom of the container receives 200 lbs push

Figure 1-1 Pressure (force per unit area) is transmitted throughout a confined fluid

COPYRIGHT (2001) EATON CORPORATIONC

1. The bottle is filledwith liquid, which isnot compressible

2. A 10 lb. force is appliedto the stopper with a surface area of one square inch

3. This results in 10 lb of force on every square inch of surface area in the container

4. If the bottom has an area of 20 sq. in. and each square inch is pushed on by 10lbs. of force, the entire bottom of the container receives 200 lbs push

Figure 1-1 Pressure (force per unit area) is transmitted throughout a confined fluid

COPYRIGHT (2001) EATON CORPORATIONCWisc on line - Pascal’s Law

50 lb of Force

2500

lbs

of F

orce

50sqin

12

Forces Proportional

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Boyle’s Law

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Wisc on line – Boyles Law

As pressure increases- volume will decrease

Charles’ Law

Pressure is Same, but volume is different

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Wisc on line – Charles Law

Atmospheric Pressure

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Pressure of the air in the atmosphere due to its weight.Area = 1 in 2

1. A colum n of a ir one square inch in cross-section and as h igh as the atm osphere

2. w eighs 14.7 pounds at sea level. A tm ospheric pressure is therefore 14.7 psia

psia0

510

15 20 253035

40

Fig ure 2-3 Atm o sp he ric p re ssure is a “he a d ” o f a irCO P YR IG H T (2001) E ATO N CO RP O R ATIO NC

Gauges Absolute pressure includes atmospheric pressure Gauge Pressure (psig) + 14.7 = Absolute Pressure (psia) (Absolute Pressure – 14.7) = Gauge Pressure

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Gauge Pressure

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Gauge is in psia if it reads 0 when exposed to the atmosphereGauge is in Gauge pressure, if it shows 14.7 (sea level) when open to atm. It has been calibrated to show atm pressureGauge pressure will be different in Denver than in MiamiThis gauge reads _________

psia

Gauge Readings

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Dual Scale – red: PSI Black: kPa 1 psi = 6.895 Pa 1000 psi = 6895 PaGauge Reading:6000 Pa = 870 psi 6 kPa = 870 psi

Directional Control Valves

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Moving part (spool) of Directional Control Valves (DCVs) connects and disconnects internal flow passages within the valve body by shifting or rotating a spool.

Fluid Control Symbols

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DCV

Types of DCVs

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• Number of ports (ways)• Number of flow paths• How internal ports can be connected (spool

positions)

“Type” is named based on the following factors:

Types of DCVs (Cont’d.)

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• Two ports• One flow path• Ports are connected (flow

path open) with spool in one position and closed when spool is in the other position.

• Gives an on-off function– Safety interlock– Isolate and connect various

system parts

Two-way directional valve:

Types of DCVs (Cont’d.)

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• Three ports• Two flow paths• A single actuator port is vented

with the spool in one position (top figure) and pressurized when spool is in the other position (bottom figure).

• Functions to pressurize and drain one actuator port

• Not generally found in hydraulic applications

– If required a four-way valve is converted to a three-way by plugging an actuator port

Three-way directional valve:

Types of DCVs (Cont’d.)

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• Four ports• Four flow paths• With the spool to the right,

actuator port A is pressurized and port B is vented to exhaust.

• With the spool to the left, actuator port A is vented to exhaust and port B is pressurized.

• Functions to cause reversible motion of a cylinder or motor

Four-way directional valve:

Fluid Control Symbols

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Typical Valve Actuators

Hydraulic Reservoirs

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Baffles to SeparateR eturn L ine from O utlet L ine

M agnetic D rain P lugsat Low P oin t(s)

Pum p In let L ine

C lean-outP late

R eturn L ineF ilte r

Large Surface A reafor C ooling

F lu id Level AbovePum p In let

Capacity o f 2-3Tim es Pum p F low

Filtered B reather Cap

S ight G auge

Figure 5.2 Baffle p la te contro ls d irection of flow in tank

C O PYR IG H T (2001) EATO N C O R PO R ATIO NC

Reservoir Parts Clean-out plates

Provides complete access to the interior of the tank for cleaning or painting

Can be installed on both ends of tank Baffle plate

Used to prevent returning fluid from directly entering the pump inlet

Installed length wise through the center of the tankForces fluid to move along the tank walls

Heat is dissipatedContaminates settleCleared of any entrained airLess turbulence in the tank

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Filters• Since the worst enemy in Hydraulic & Pneumatic

components is contamination, filters are placed in the system.

• The main parts of a filter are the flange, which connects the filter

to the piping the element, which traps contamination the bowl (or housing) which seals the element.

As the element accumulates contamination, flowthru the filter decrease, causing a greater back-pressure.

When backpressure increases, usually by 5 psig, the filter must be changed

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Flange

Bowl

Element

Air Line Filters

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• Installed in the airline downstream of the dryer/separator near the connection for a tool or actuator

• As the air enters, a deflector plate causes the air to swirl.

• Centrifugal force throws water and solid particles to the wall.

Filter Replacement

Filter condition indicators Electrical or visual indicators when

the element backpressure indicates clogging

Filter bypass valve Incorporated into the housing to

eliminate the possibility of element collapse or rupture when the element becomes clogged or when the fluid is very viscous

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Filter bypass valve and filter condition indicators

Filters

Over 80% of hydraulic system failures are due to poor fluid conditionSources of contamination Built in contamination

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Proper care of hydraulic fluid, both in system and in storage and handling, has an effect on machine performance and system endurance.

Reservo ir

C ylinders

F ittings

Pum ps

H oses

Valves

M anifolds

F igure 6-1 Sources of built-in contam inationCOPYR IG HT (2001) EATO N COR POR ATIO NC

Filters (Cont’d.)

Sources of contamination Ingressed contamination

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OILService

NewO il

F ill Cap

C leanoutP late

CylinderRod Seals

Fig ure 6-3 So urc e s o f ing re sse d c o nta m ina tio nC O P YR IG H T (2001) EATO N C O R PO R ATIO NC

Factors Affecting Pneumatic Fluid Power System Efficiency

Air leaks Improper compressed air usage High compressor power or motor current Moisture in system Oil in air High pressure drop across components

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Factors Affecting Hydraulic Fluid Power System Efficiency

• Contamination of hydraulic fluid• Slow hydraulics due to oil breakdown• Weak hydraulics due to overheating• Pressure control valve failure• Directional control valve failure• System leaking fluid• Clogged valves, hoses and lines

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Wisc on line – hydraulic oil contamination

Pumps

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Introduction to Pumps

A simple description of Pumps is that they are used to move fluids from one location to another location.

Pumps add energy to these fluids to move them from one location to another location.

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Positive Displacement (PD) Pumps

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Vane Gear Diaphragm

PeristalticVariable Displacement

Screw

Introduction to Pumps (Cont’d.)

Pumps come in many types and sizes, from small metering pumps that pump ounces per day to high-capacity pumps that pump thousands of gallons per hour.

Pumps are widely used in industry and are a large part of the maintenance workload.

Pump failure is a major cause of downtime and lost production.

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Introduction to Pumps (Cont’d.)

Primary TYPES of pumps are: Positive Displacement (PD) Centrifugal

Different types and sizes of each category. Each type is designed for a specific application. Failure of pumps can cause a number of problems,

therefore it is important to use the: Correct type Correct size Proper installation

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Introduction to Pumps (Cont’d.)

Pump failure is usually attributed to improper installation, or a poor maintenance program.

Even if a pump is installed properly and maintained, pumps can breakdown.

Proper installation, repair, and maintenance of pumps represents a significant part of a good preventive maintenance program.

Note that the pump manufacturer's manual is required for detailed installation, maintenance and troubleshooting information.

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Pump Types Pumps are classified as either centrifugal or positive-displacement.

Centrifugal pumps have the following characteristics: Used for pumping liquids that have relatively low viscosity

(thin and fast flowing). Relatively Low-pressure pumps. Uses centrifugal force to create a constant stream of fluid.

Positive-displacement pumps have the following characteristics:

Used for pumping liquids that have very high viscosities (thick and slow flowing).

High-pressure pumps. Takes an amount of liquid and moves it physically from one

place to another. Produces a pattern of intermittent flow. The liquids flow in

intervals: flow/no-flow.

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Workings of Positive Displacement Pump

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Atm osphericPressure

In let Phase O utput Phase

In let

O utle t

to c ircuit to c ircuit

A tm osphericPressure

In let

O utlet

F igure 15-3 Positive d isplacem ent pum pCO PYRIG H T (2001) EATO N C O R PO RATIO NC

Reciprocating PD PumpsPressure Washer Pump: Provides high-pressure water, ideal for cleaning and

sanitizing. Pressure washer pumps can be belt, direct, or

gearbox driven.

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Rotary PD Vane Pump

Develops a relatively smooth flow

Pressure applied is only as great as the least resistance to the flow in the system.

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Most common positive displacement pump found in a machine’s hydraulic system:

1

2

34

3

270°

0°

90°

180°

Centrifugal Pumps A centrifugal pump operates by increasing the

velocity of a liquid. Fluid entering the pump’s inlet is rotated by an

impeller. This rotation creates “Centrifugal Force” within a

stationary casing.

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OutletImpeller

InletShaft

Centrifugal Pump Example

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Centrifugal Pumps (Cont’d.)

Pump casing: The case surrounds the shaft, bearings, packing gland, and impeller. Pump casings are split or solid in design.

Suction port: The location where fluid enters the pump. Discharge port: The location where fluid is discharged from the pump. Pump shaft: The bearing-supported shaft turns the impeller and is usually

coupled to a motor.

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Vertically Split Case

Centrifugal Pumps (Cont’d.)

Bearings: Support the shaft and impeller in the casing. Impeller: The rotating part that increases the speed of

the fluid. Impellers come in many different types and are used for different purposes.

Impeller vanes or blades: Part of the Impeller that directs the flow of fluid within the pump.

Impeller shroud: The shroud encloses the impeller blades and keep the flow of fluid in the impeller area.

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Vertically Split Case

Centrifugal Pumps (Cont’d.)

Wear rings: Replaceable rings used in some pumps to allow some fluid leakage between the impeller and the casing in the suction area. The leakage makes a hydraulic seal and helps the pump operate more efficiently.

Packing gland: Contains an adjustable follower that exerts force upon the packing to control fluid leakage around the shaft.

Mechanical seal: Seals the fluid flow in the pump. Seals are used instead of packing in some pumps.

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Vertically Split Case

Centrifugal Pump Cavitation Cavitation is an abnormal condition that

can result in loss of production, equipment damage and worst of all, personnel injury.

Occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities (bubbles) where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shockwave.

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Cavitation Steps

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Cavitation (Cont’d.)

 

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Cavitation (Cont’d.)

Impeller Cavitation Regions

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Cavitation (Cont’d.)

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Cavitation Primary Cause:Low suction pressureCavitation can result in:

Loss of capacity Lowered Discharge Pressure Lower Efficiency Noise, Vibration, and Damage to Pump

components

Cavitation (Cont’d.) It is often heard as a rumbling sound coming from

the pump.  The collapsing bubbles cause mini-implosions that

tear metal out from impellers and volutes. 

Wisc on line - cavitation

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Collapsing Bubbles

Cavitation Damage

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Cavitation Summary

Vaporization of the liquid (bubble formation) occurs due to the reduction of the static pressure to a value below that of the liquid vapor pressure.

The reduction of static pressure in the external suction system occurs mainly due to friction in suction piping.

The reduction of static pressure in the internal suction system occurs mainly due to the rise in the velocity at the impeller eye.

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General Pump Maintenance

Leaks Excessive noise Loss of Pressure Overheating Importance of Good PM system

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Safety Considerations LOTO SDS PPE High Pressures Supervisor’s Direction Clean Up Documentation

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Summary Hydraulic/Pneumatic

Systems Fluid Laws PSIA / PSIG Filters DCV’s

Pumps 2 Types of Pumps General Pump

Maintenance62/61

QUESTIONS ?

Orlando Moreno+1 770.354.3072omoreno@hotmail.com