pump and compressors

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1. Wecture Five

Pumps and Compressors

Pumps and compressors are primary sources
of flow in fluid power systems. Maximum
system horsepower is controlled by the size of
these components along with system flow.
The three basic types of pumps are the Gear,
Piston, and Vane designs.

(Mis tolloi0snydemie tormentas
4) relitionstip bebyyeen Elorsepoyer,
Pressure, and Plow,

Hydraulic Horsepower = GPM x PSI x .000583

2. HYDRAULIC PUMPS AND POSITIVE
DISPLACEMENT

In its most basic sense, positive displacement means what
you take in you put out. In other words, for each

reyolution of a hydraulic pump of this type, a specific
quantity of fluid is produced relating to the displacement
of the pump.

3. The Rule of 1500

Mhe role of 150015 4 engineering reference to a predictable
relationship between Horsepower, How, and Pressure. This 15 used
when sizing an electric motor for a particular hydraulic system.

In any hydraulie system operating ata pressure of ISD) psi, every
GP of How produeed by the pump will require at lest one
>) This relationship is linear = in other
words, at a pressure of 750 psi, each GPM of flow would require

Y horsepower. At 3000 psi, each GPM would need 2 horsepower,
and soon.

In pneumatic systems there is asimilar relationship. However,
Since tie relationship is nov linear (because all compresses), the
math requined to) calculatertis beyond the scope of this Course:

4. Pumps and Compressors

Betore we goany firtier ie shold be pomted Onp tat no matter
Wha design Ol pimp) Or compressoris bene discussed, alll pimps
produce flow the same way.

Pumps and compressors produce flow by creating a “pressure
differential.” Fluids always flow from a higher pressure to a lower
pressure. By using the increasing pump volume at the inlet, the
pump (or compressor) creates a region of decreasing inlet pressure

(vacuum). This causes the higher reservoir pressure (atmospheric) to
push the fluid to the lower pressure inlet area. An example would be
a person drinking water through a straw. One sucks, creating a
lower pressure (vacuum) inside the mouth, and the higher
(atmospheric) pressure on the liquid surface pushes it up the straw.

dhe tinidis trapped inside the pump, and it 1s carried) to the outlet
where the yolumeis decreased and pressure increased. lid willl
fake the path ofdeast resistance, which Is out tie device outlet,

5. Pumps and Compressors

Hydraulic Pump Symbol ’ en

Symbol

Its important to note that the above symbols do not indicate a
specific design type, just function. As you can see, the only
difference is the triangle, Remember, pumps and compressors)
only produce OW. Pressure is created by resistance to that
flow, If thereis no resistance, 110 moves av abmospheric)
Pressure, ana eres mo Gage) pressure,

6. Vane Pumps

In the above illustration, only the internal parts are shown.
Normally, one port would be connected to the “increasing” yolume
side and another port would be connected to the “decreasing”
yoluime side; The outer piece (Called the cam rings) does nob move;
The center piece (the rotor) rotates and is off center The dark
lines are the “yanes They moye in and ont because of centrifugal)
force to MAIN EAN a enla gatas tie camialigy

7. Vane Pumps

ii Decreasing
Increasing

Volume

Ic pump ope:
dio aná
das nin y
LOMME VOIS AS LE

CSICA PIN presa!

8. Vane Pumps

As the fluid! passes from left to right it becomes “trapped” between
the rotating group and'the pump housing. It is carried around to the
outlet port. There, the volume containing the fluid decreases, causing
the pressure to increase, Eluids always take the path of least
resistance (as does electricity)so out to the system ib goes, All
PMPs oyarite to Mis mmanncmncearclcss orilosta nor dont iia LONE

9. Balanced Vane Design

The previous slides showed normal yane pump. In normal operation
vane and gear pumps are loaded” to one side because of pressure at
the outlet port. This Joading” has an adverse effect on bearing life.
A balanced vane pump hasiits ports located in four distinct locations)
around shato(2inletsyand! 2 ouvlets, cach 160) apart) to) balance
thetonces onthe SNA dhe resultas extended! beaning service lites

10. Cartridge Assembly,

A lot of manufacturers of fixed displacement vane pumps have
incorporated the rotating group into a remoyable assembly that
can be replaced independently of the housing, so piping can
remain) connected, This assembly, called a “cartridges Consists of:
the rotor, vanes, cam ring and port plates, It minimizes down time
tonebmild ay pimp) and meduces piping leaksuni the systems,
Carinidge assemblies ane rarely sedan Unbalanced) yane pimps:

11. Double Pump

Schematic symbol for a double pump

Although vane pumps are sometimes put together in pairs to
form a “double pump,” any design could be made a double
pump. All this means is that you have two pumps driven by one
motor which may have their flows put together or separated.
Typically, one of the pumps is several'times larger than the
other, sothe larger pump) will produce much more flow. An
application for this type of pump mill be discussed mm Unit 11°

12. Variable Volume Vane Pump

“Variable volume” means that the “amount” of oil
which is displaced by a pump each revolution can
change whereas in other “fixed” displacement models
it cannot. What controls the “total amount” of oil
(flow = GPM) produced by atixed displacement pumpy,

Speed and Displacement

13. Variable Volume Vane Pimp) Operation

Cam NOTE; Port Plate
Not Shown

NN

Screw
Adjustment

Thrust Bearing
Variable Volume Vane Pump

The key to understanding

his illustration is knowing th:

5

Centened yi
Pressiine is mantamco hc rotor traves paste camino
esutevlins from ones stilo to fue Oller toy rave t

14. Volumetric Output of a Pump

Theoretical Pump Flow = Speed x Displacement
231

What this means is that if there is no internal mechanical
mechanism that changes the displacement volume
causing flow rate change, the only two things that control!
flow from a pump are the physical/size of the pump and
how fast you run it,

15. Pressure Compensated Variable
Volume Vane Pump Operation

Spring Adjustment

Pressure Compensated
Vane Pump

As pressure builds in the system it is felt everywhere including the
pump outlet. As outlet pressure rises, the cam ring willl push away
from the pressure direction toward! the path of least resistance which
isthe spring, When the pressure of the system is equall to the tension
ofthe spring, the rotor will be in the centen of the cami ring, den
flow williStopyyhilespressune in) the systems maintained as
dloformined dy ihe sopas adjusimont

16. Pressure Compensated
Variable Volume Vane Case
Drain

All pumps) experience internal leakage butitis worst in the:
modelsillustrated here, Toalleyiate the mtemial pressure
caused by this leakage, a case drain is) provided: his
relieyesitheantemnalpressuresand prevents bic TON scallion
LC Dilip shit trom Dloytoy ou,

17. Gear Pumps

In a gear pump, an increasing yolume (therefore, decreasing
pressure) is generated as teeth un-mesh or moye away from each
other The tind drawniinto the pump miler from thie reseryorn is)
forced around! the teeth toward the pump outlet, nov tinoneh) the)
middle, As the teeth move toward each other, the volume decreases,
and theincreasing pressune ONCE Mie MiG OUL Die oulst ports

18. Piston Pumps

There are two major categories of pumps: Axial and
Radial.

Asxial(Swastiplate)piston pump,

19. Piston Pumps

Illustrated|aboye are examples of Radial piston pumps. Their pistons meet the drive
shaft axis at 90 degrees. They are more compact yielding space sayings and can be ran
Ata wide speed|range, Asmotors, they are very popular in cabling systems.

20. Piston Pumps

Piston pumps operate under the same controlling principles as all
other pumps. With this design, a piston moves back and forth in a
barrel. As the piston moves back, a larger volume is created that
provides a vacuum, As the piston moyes forward, the volume is
decreased (pressure increases) and fluid is forced! out. Axial/piston:
pumpsjhaye pistons that moyen parallel to the drive shaft axis;
Radialpıston pumps have pistons thabmoye av 90\degrecs to the
drive stiatvaxis, Axial piston Pumps ane, Dy tat, themmost- common,
cr pecan po made variable volume Dy adjusting Dic amount
OFSiroie te piston travels in the eylindse bore,

21. Pressure Compensated Axial Piston
Pump

Full Flow Pressure Compensated
Piston Pump

‘System Pressure
Sensed Here

ane) on

Compensator fires at pressure
setting- no flow

Low pressure-full stroke condition

In the axial pump above, a pressure build! up causes the
compensator rod to push against the swash plate which in turn
decreases the stroke of the pistons, This reduces amount of flow to
zero when the pressure completely balances the tension of the
Spring, in the same maneras the variable volume pressure
Compensated vane PUMP ane Symbols One Pressure
Compensated ano and piston pumps are wie sao,

22. Oyer-centen (reversible) Axaal
Piston Pumps

As in the vane pump, reverse flow in the piston pump is
accomplished by moving the rotating group beyond a
“center” point. In the piston pump the swash plate is the
member that moyes to + or — 0 degrees to achieve this
feature. These types of pumps are often found in hydrostatic
transmissions, he symbol above is couldindicate any the
piston and vane pump with reyerse flow capability. ihe
description onthe component on the\system) schematic would:
tell theytechniGianithe detailsordieypump) seas

23. (Compressors

Compressors operate by drawing in air at lower than atmospheric
conditions and then trapping, and compressing it. Once
compressed, the air is allowed to escape to the path of least
resistance, usually into the receiver tank. Compressors create flow
using the same differential pressure principles as pumps do, but
the fluidis a gas. Pump and Compressor symbols are identical,
except for the flow arrow. In both cases, the arrow points “out” of
the deyice; indicating flowy is produced) Hon pumps, the arrowAs
solid|=1or compressors, transparent, hora quick determination it,
Aschemaucishydranlic Onpnenmauc, tind Mco producer
Syibob Solid ts hydric tens paront ls pustlueltte,

24. (Compressors

Compressors

Dynamic Displacement

Reciprocating

. FE

Crosshead Labyrinth
Free Piston Diaphragm

E

Disvhiesment

25. Dynamic Compressors

Dynamic compressors are not positive displacement. They move air
by adding kinetic energy to it or in other words they “throw” the air.
Examples of dynamic compressors would include a leaf blower, hair:
dryer, and common fan. Dynamic compressors are primarily used!
for low pressures but high yolumes of air. Dynamic compressors
(fans) are yery common at low, pressures, When typical pneumatic
system pressures are required, their high cost limits applications to
on irecamn requirements such as in tie 100d and pharmaceutical
Andusirtos A jor ongine ls anote" elle Of delle compressor

26. Displacement Compressors

Standard displacement compressors can be single stage
where the air is compressed once or multi-stage where
the airis compressed! two) or more times to achieve
highen efficiency. In operation, alr is. drawn in as the
piston moyes doy. When the piston moyes pair is
compressodandinon released ro ino receiver is

27. Multi-=stage Compressors

In multi-stage compressors, air is compressed twice in order to get it
to the receiver tank at a higher pressure but lower temperature. The
hot compressed! air is cooled atten the first stage in an intercooler
to reduce the air temperature entering the next stage, Since the
Cntening alle temperatures lower Hie OU eL all temperatures also)
lower Single stage COmpnessionis less ortletent Deenliss ore heal:
has) to bewiven upan tie receiver which tianslates nto lost presse,

28. Screw Compressors

© One-piece housing

bearings -
Saremaly long
is

Dry and! Oillilooded|

29. Screw Compressors

30. Oil Separation

31. Reyiew

Explain the purpose of the pump.

List three different types of pumps.

Assuming fixed displacement, what two things determine the flow rate of a pump?

What is the relationship between flow and input horsepower?
What is the rule of 1500?

Name the major internal components of a vane pump assembly.
What type of vane pump is balanced?

What is pressure compensation?

What is the purpose of a case drain in a hydraulic pump?

What is the difference between a axial piston pump and a radial piston pump?
What compressor type is the most common?

What is multi-staging?

Why is multi-staging more efficient?

What is a dynamic compressor?

What is the most common use for dynamic compressors?