Hydraulic (hydraulic principle)
Hydraulic machinery are machines and tools that use fluid power to do work. Heavy equipment is a
In this type of machine, high pressure fluid - called the hydraulic fluid - is transmitted throughout the
machine to various hydraulic motors and hydraulic cylinders. Fluid controlled directly or
automatically by control valves and distributed through hoses and tubes.
Hydraulic engine popularity is due to a very large amount of power that can be transferred through
small tubes and flexible hoses, and high power density and variety of actuators that can harness this
Hydraulic machine is operated using hydraulic, where the fluid is powering the media. Pneumatics,
on the other hand, based on the use of gas as a medium for power transmission, generation and
Force and torque multiplication
Fundamental feature of the hydraulic system is the ability to apply force or torque multiplication in a
way that is easy, depending on the distance between the input and output, without the need for
gears or mechanical lever, either by changing the effective areas in the two connected cylinders or
the effective displacement ( cc / rev) between pump and motor. In normal cases the ratio of
hydraulic combined with mechanical strength or the ratio of the design optimum engine torque, as
in the movements and trackdrives booms for excavators.
(1) Two hydraulic cylinders are interconnected:
Cylinder C1 is one inch radius, and the cylinder C2 is ten inches in radius. If the force exerted on C1 is
10 lbf, the force exerted by C2 is 1000 lbf because C2 is a hundred times larger in area (S = πr ²) as
C1. The downside to this is that you must move the C1 hundred inches to move C2 one inch. The
most common use for this is a classic in which a hydraulic jack pump with a small diameter cylinder
that is connected to the lift cylinder with large diameter.
(2) Pumps and motors:
If a hydraulic rotary pump with a displacement 10 cc / rev connected to a hydraulic rotary motor
with 100 cc / rev, shaft torque required to drive the pumps is 10 times smaller than the available
torque at the motor shaft, but shaft speed (rev / min) for motor is 10 times smaller than the speed
of the pump shaft. This combination is actually the same type of force multiplication as an example
of the cylinder (1) only that the force is linear in this case is a rotary style, which is defined as the
Both examples are commonly referred to as a hydraulic or hydrostatic transmission which involves
the transmission of certain hydraulic "gear ratio".
A simple open center hydraulic circuit.
A simple open center hydraulic circuit.
The equivalent circuit sistem matik
For the hydraulic fluid to do work, it must flow to the actuator and or motors, then return to the
reservoir. The fluid is then filtered and pumped back. The road taken by so-called hydraulic circuit of
hydraulic fluid that there are several types. Open center circuits use pumps which supply a
continuous flow. The flow is returned to the tank through the central control valve is open, ie when
the valve centralized control, it provides an open path back to the tank and the fluid is excited to
high pressure. Otherwise, if the control valve is actuated it routes fluid to and from the actuator and
tank. Fluid pressure will rise to meet resistance, because the pump has a constant output. If the
pressure rises too high, the liquid back into the tank through a pressure valve. Multiple control
valves may be stacked in series . This type of circuit can use inexpensive, constant displacement
Center closed-circuit supply full pressure to control valves, actuated valves is there or not. Pumps
vary their flow, pumping very little hydraulic fluid until the operator actuates a valve. The valve's
spool so it does not require a central opening to the tank return line. Some valves can be connected
in parallel and the pressure regulating system is the same for all valves.
Constant pressure and load-sensing systems
Center of the closed circuit exists in two basic configurations, usually associated with a variable
regulator to pump the oil supply:
Constant pressure systems (CP-system), standard.Tekanan pump is always equal to the pressure
pump to the regulator setting. These arrangements should include the maximum required load
pressure. Pumps provide flow in accordance with the required amount of flow to the consumer. CP-
system generates great power losses if the machine works with large variations in load pressure and
the pressure of the system average is much lower than the setting pressure to the pump regulator.
CP simple design. Works like a pneumatic system. The new hydraulic functions can be easily added
and quickly respond to system.
Constant pressure systems (CP-system), is derived. The same basic configuration as the 'standard'
CP-pump system but dismantled for low stand-by pressure when all valves are in neutral position.
Not so fast a response as the standard of living pump CP but a prolonged time.
Load-sensing system (LS-system) result in less power loss as the pump can reduce both the flow and
pressure according to load requirements, but require more tuning than the CP system to system
stability. LS-systems also require additional logic compensator valve and directional valve in the
valve, so it is technically more complicated and more expensive than the CP system. LS-system that
the system generates a constant power losses associated with a decrease in pressure regulator set
for the pump:
Power loss = \ Delta Pi (LS) \ cdot Q (tot)
ΔpLS average is about 2 MPa (290 psi). If extra high flow pumps such losses can be considered.
Power loss is also increased if the load pressure varies a lot. Cylindrical region, the motor
displacement and torque of the mechanical arm must be designed to adjust the load pressure in
order to reduce power losses. Pump pressure is always equal to the maximum load pressure when
some functions are executed simultaneously and the input power to the pump equals (max. load
pressure ΔpLS +) x number of streams.
Five basic types of load-sensing system
(1) Load sensing without compensators on the directional valve. Hydraulically controlled LS-pump.
(2) Load sensing with up-stream compensator for each connected directional valve. Hydraulically
(3) Load sensing with downstream compensator for each connected directional valve. Hydraulically
(4) the burden felt by the combination of upstream and downstream compensator. Hydraulically
(5) Load sensing with a synchronized, well-controlled electrical pumpdisplacement and valves
controlled the flow of electricity to the area quicker response, improved stability and less system
losses. This is the new LS-type system, not yet fully developed.
Technical compensator installed in the downstream physical valveblock can be installed "upstream",
but works as a compensator downstream.
Type of System (3) gives the advantage that the function is activated independently synchronized to
the pump flow capacity. The flow relationship between two or more functions enabled to remain
independent of load pressure even if the pump reaches the maximum swivel angle. This feature is
important for machines that often run with the angels and the maximum rotary pump is activated by
several functions that must be synchronized in speed, such as the excavator. Type (4) system, the
function of the compensator headwaters have priority. Example: Steering-wheel loader to function.
This type of downstream system with compensators typically have a unique trademark, depending
on valve model, eg "LSC" (Linde Hydraulics), "LUDV" (Bosch Rexroth, Hydraulics) and "Flowsharing"
(Parker Hydraulics), etc. No official name for the standard this type of system has been established
but Flowsharing is a common name for it.
Open and closed circuits
Open loop and closed loop circuits.
Open-loop: Pump-inlet and-back motor (via the directional valve) connected to a hydraulic loop
tank.The term applies to feedback; more precise term that is open versus closed "circuit".
Closed loop: Motor-return is directly connected to the pump inlet. To keep the pressure on the low
pressure side, a charge pump circuit (gearpump small) that the supply of oil is cooled and filtered
into the low pressure side. Closed-loop circuit, commonly used for hydrostatic transmissions in
mobile applications. Advantages: No-way valves and a better response, the circuit can work with
higher pressure. Angle rotary pumps include both positive and negative direction of flow.
Disadvantages: pump can not be used for other hydraulic functions in an easy and cooling can be a
problem because of the limited exchange of oil flow. High power closed system in general should
have a 'flush-valve' assembled in series in order to exchange more flow from the basic leakage flow
from the pump and motor, to increase cooling and filtering. A flushing valve is usually integrated in
the motor housing to get the cooling effect for a rotating motorhousing oil itself. Losses in the motor
housing from rotating effects and losses in the can ballbearings quite as motorspeeds will reach
4000-5000 rev / min or even more at maximum vehicle speed. Leakage flow and flush out additional
flow must be supplied by the charge pump. The cost of the pump is thus very important if the
transmission is designed for high pressure and high-speed motor. High oil temperature, usually a big
problem when using high-speed hydrostatic transmission vehicle for longer, for example when
transporting the work machine from one place to another. Oiltemperatures high for a long time will
drastically reduce the life time for transmission. To keep oil temperatures down, the pressure during
the transportation system must be lowered, which means that the minimum displacement for the
motor should be limited to a reasonable value. Circuit pressure during transport between 200-250
bar is recommended.
Closed-loop system of mobile devices, commonly used for transmission as an alternative to
mechanical and hydrodynamic (converter) transmission. The advantage is Stepless gear ratio
('hydrostatic' gear ratios) and more flexible control of the gear ratio depending on load and
operating conditions. Hydrostatic transmission is usually limited to about 200 kW max. power as the
total cost is too high at higher power in comparison with hydrodynamic transmission. Such a large
wheel loader heavy machinery and therefore are usually equipped with a converter transmission.
Recently the technical achievement for the transmission converters have improved efficiency and
developments in software also improve the characteristics, such as gear shifting programs to choose
from for more operating devices and measures, giving them characteristics close to the hydrostatic
Hydrostatic transmission for earth moving machines, such as for tractor loader, often equipped with
an 'Inch pedal' which is used to temporarily increase the rpm of diesel engines while reducing vehicle
speeds in order to increase the available hydraulic power output for the working hydraulics at low
speeds and increases tractive effort . Function similar to stalling a converter gearbox at high engine
rpm. Inch-function that affects the characteristics of the presets for the 'hydrostatic' gear ratios
versus the diesel engine rpm.
An exploded view of an external pump equipment.
Pump supplies hydraulic fluid to the components in the system. The pressure in the system
developed in reaction to the load. Therefore, a pump capacity of 5,000 psi to maintain the flow
against the load of 5,000 psi.
The pump has a power density of approximately ten times larger than the electric motor (by
volume). They are powered by an electric motor or engine, connected by gears, belts, or a flexible
elastomeric coupling to reduce vibration.
Types of hydraulic pumps for hydraulic machinery applications;
* Gear pump: cheap, durable, simple. Less efficient, because they are a constant displacement, and
particularly suitable for pressures below 20 MPa (3000 psi).
* Vane pump: cheap and simple, reliable (especially in the form of rotor g). Good for higher-flow low
* Axial piston pump: many are designed with variable displacement mechanism, to vary the output
flow for automatic control of pressure. There are a variety of axial piston pump design, including a
swashplate (sometimes referred to as valveplate pump) and checkball (sometimes referred to as a
vibrating plate pump). The most common is the pump swashplate. A variable-angle swash plate
causes the piston to reciprocate.
* Radial piston pump A pump that is usually used for very high pressure on small streams.
Piston pumps are more expensive than the equipment or vane pumps, but provide longer operating
life at higher pressures, the fluid is difficult and long continuous duty cycle. Pump piston forming one
half of the hydrostatic transmission.
Fluid direction control valve actuator desired route. They usually consist of the spool in a cast iron or
steel housing. Spool slides to different positions in the housing, a cross grooves and channels route
the fluid based on the position of the spool.
Spool has a center (neutral) position maintained with springs; in this position the supply fluid is
blocked, or returned to the tank. Spool shifts to one side of the route hydraulic fluid to the actuator
and provides a return path from the actuator to the tank. When the spool is moved in the opposite
direction of supply and return path enabled. When the spool is allowed to return to the neutral
(center) position the actuator fluid paths are blocked, locking it in position.
Directional control valves are usually designed to be stacked, with one valve for each hydraulic
cylinder, and one fluid input supplying all the valves in the stack.
Very tight tolerances to handle high pressure and avoid leaking, spools typically have a housing
permit less than a thousandth of an inch (25 μm). Block valves will be mounted to the frame of the
machine with a three point pattern to avoid distorting the valve block and valve congestion sensitive
The position of the spool can be actuated by mechanical levers, hydraulic pilot pressure, or solenoids
which push the spool left or right. A seal allows part of the spool protruding outside the housing,
which can be accessed by the actuator.
Block main valve is usually a pile of rack-way flow control valve is selected by the capacity and
performance. Some valves are designed to be proportional (flow rate proportional to valve position),
while others may simply be an on-off. Control valve is one of the most expensive and sensitive parts
of the hydraulic circuit.
* Pressure relief valves are used in several places in the hydraulic machine; on the circuit back to
maintain a small amount of pressure for brakes, pilot lines, etc. .. In hydraulic cylinders, to prevent
overload and the hydraulic line / seal broken. On the hydraulic reservoir, to maintain a small positive
pressure, including moisture and contamination.
* Pressure reducing valve reduces the supply pressure required for the various circuits.
* Sequence control valve series hydraulic circuit, to ensure that one of the hydraulic cylinder is fully
extended before starting again strokenya, for example.
* Shuttle valves provide a logical or function.
* Check valve in one direction, allowing to charge the accumulator and maintaining pressure after
the engine is off, for example.
* Pilot controlled Check valves are one-way valve can be opened (for both directions) by a signal to
foreign pressure. For example if the load should not be continued by another check valve. Often
foreign pressure from the other pipe that is connected to the motor or cylinder.
* Counterbalance valve is actually a special type of pilot-controlled valve. While the valve is open or
closed, the counterbalance valve acts a bit like a pilot-controlled flow control.
* Cartridge valves are in fact part of a check valve, they are components of the rack with standard
envelopes, making them easy to populate a proprietary valve block. They are available in many
configurations, on / off, proportional, pressure relief, etc. They generally screw valve block and
electrically controlled to provide logic and automated functions.
* Hydraulic fuses are in-line safety devices designed to automatically shut down the hydraulic lines if
the pressure becomes too low, or safely vent fluid if pressure becomes too high.
* Auxiliary valve. Complex hydraulic systems usually have auxiliary valve blocks to handle various
duties unseen to the operator, such as accumulator charging, cooling fan operation, AC power, etc.
They are usually valves designed specifically for a particular machine, and can consist of a metal
block with ports and channels drill. Cartridge valve is threaded into the port and can be controlled by
electrical switches or a microprocessor to route fluid power as needed.
* Hydraulic cylinders
* Rotary actuator (hydraulic)
* Hydraulic motor (pump plumbed backwards)
* Hydrostatic transmission
Hydraulic fluid reservoir holds excess hydraulic fluid to accommodate volume changes of: cylinder
extension and contraction, temperature driven expansion and contraction, and leaks. Container is
also designed to assist the separation of air from the fluid and also works as a heat accumulator to
cover losses in the system when peak power is used. Design engineers are always pressured to
reduce the size of the hydraulic reservoir, while equipment operators always appreciate larger
Some designs include dynamic fluid flow channels on the back roads that allow for a smaller
Accumulator is part of the Common hydraulic machinery. Their function is to save energy by using
pressurized gas. One type is a tube with a floating piston. On one side of the piston is pressurized
charge of gas, and on the other side is a liquid. The bladder is used in other designs. Keep a backup
of fluid systems.
Examples of the accumulator is used for backup power steering or brakes, or to act as a shock
absorber for the hydraulic circuit.
Also known as a tractor fluid, hydraulic fluid is the life of the hydraulic circuit. Usually oil with various
additives. Some hydraulic machines require fire-resistant fluids, depending on their applications. In
some factories where food is prepared, water is used as the working fluid to the health and safety
In addition to transferring energy, hydraulic fluid needs to lubricate components, suspending,
contamination and metal powders for transport to the filter, and to function well for several
hundred degrees Fahrenheit or Celsius.
Filters are an important part of the hydraulic system. Continuous metal particles generated by
mechanical components and need to be removed along with other contaminants.
Filters can be positioned in many locations. The filter may be located between the reservoir and the
pump intake. Blockage of the filter will cause cavitation and possible pump failure. Sometimes the
filter is located between the pump and valve control. This arrangement is more expensive, because
the filter housing pressurized, but eliminates cavitation problems and protects the control valve
from pump failure. The third common location just before the line filter back into the reservoir. This
location is relatively insensitive to clogging and does not require a pressurized housing, but the
contaminants that enter the reservoir from an external source is not filtered up through the system
at least once.
Tubes, Pipes and Hoses
Hydraulic tube seamless precision steel pipes, specially made for the hydraulics. The tubes have
standard sizes for different pressure ranges, with standard diameters up to 100 mm. Tubes are
provided by the manufacturer in a length of 6 m, cleaned, oiled and mounted. The tubes are
interconnected by various types of flanges (especially for larger sizes and pressures), welding cones /
nipples (with o-ring seal), several types of connections and flare cut-rings. Larger size, hydraulic pipe
used. Jump to join the tube welding is not acceptable because the interior can not be checked.
Hydraulic pipe used in case standard hydraulic tubes are not available. This is generally used for low
pressure. They can be connected with threaded connections, but usually by the welds. Due to the
larger diameter pipe can usually be inspected internally after welding. Black pipe is non-galvanized
and suitable for welding.
Hydraulic hose rated by pressure, temperature, and fluid compatibility. Hose is used when the pipe
or tube can not be used, usually to provide flexibility to the operation or maintenance of machinery.
Constructed with rubber hoses and steel layers. Rubber interior is surrounded by numerous layers of
woven wire and rubber. The exterior is designed for abrasion resistance. The fingers bend hydraulic
hose carefully designed into the machine, since hose failures can be deadly, and violating hose
minimum bend radius will cause failure. Hydraulic hoses generally have steel swaged on the end
equipment. The weakest part of the high pressure hose is the connection of the hose to fit. Another
drawback of the hoses is the shorter life of rubber that require periodic replacement, usually at
intervals of five to seven years.
Tubes and pipes for hydraulic applications are internally oiled before the system is commissioned.
Usually painted steel pipe outside. Where the flare and the other clutch is used, the paint will be
removed under the nut, and is the location where corrosion can begin. For this reason, in most
marine applications piping is stainless steel.
Seals, fittings and connections
Secara umum, katup, silinder dan pompa memiliki bos threaded perempuan untuk sambungan
fluida, dan selang telah berakhir dengan tawanan wanita gila. Seorang laki-laki, pas dipilih
untuk menghubungkan dua. Banyak sistem standar digunakan.
Peralatan melayani beberapa tujuan;
1. Untuk jembatan standar yang berbeda; O-ring bos untuk JIC (hidrolis), atau pipa benang
menghadapi segel, misalnya.
2. Untuk memungkinkan komponen orientasi yang tepat, sebuah 90 °, 45 °, lurus, atau putar
pas dipilih sebagai diperlukan. Mereka dirancang untuk diposisikan dalam orientasi yang
benar dan kemudian menegang.
3. Untuk menggabungkan sekat hardware.
4. Pas melepas cepat dapat ditambahkan ke sebuah mesin tanpa modifikasi dari selang atau
Tipikal bagian dari alat-alat berat mungkin telah ribuan titik-titik sambungan disegel dan
* Pipe fitting, pemasangan yang kacau sampai ketat, sulit untuk mengarahkan sebuah miring
pas benar tanpa atas atau di bawah pengetatan.
* O-ring bos, yang cocok adalah mengacaukan menjadi bos dan berorientasi sesuai
kebutuhan, mengencangkan mur tambahan pemasangan, mesin cuci dan o-cincin di
* Flare segel, logam cap kompresi untuk logam dengan sebuah kerucut dan suar kawin.
* Face seal, flensa logam dengan alur dan o-cincin yang diikat bersama-sama.
* Beam segel, yang mahal untuk logam logam cap digunakan terutama dalam pesawat
* Swaged stempel, tabung dihubungkan dengan peralatan yang swaged secara permanen di
tempat. Terutama digunakan dalam pesawat terbang.
Elastomeric stempel (O-cincin wajah bos dan segel) adalah yang paling umum jenis anjing
laut dalam alat-alat berat dan mampu diandalkan penyegelan 6000 + psi (40 + MPa) tekanan
Daya hidrolik didefinisikan sebagai Arus x Tekanan. Kekuatan hidrolik yang diberikan oleh
sebuah pompa: P dalam [bar] dan Q dalam [menyalakan / min] => (P x Q) ÷ 600 [kW]. Ex.
Pompa memberikan 180 [menyalakan / menit] dan P sama dengan 250 [bar] => Pompa daya
output = (180 x 250) ÷ 600 = 75 [kW].
Ketika menghitung input daya ke pompa, efisiensi total pompa ηtotal harus disertakan.
Efisiensi ini merupakan hasil dari efisiensi volumetrik, ηvol dan hydromechanical efisiensi,
ηhm. Power input = Power output ÷ ηtotal. Rata-rata piston pompa aksial, ηtotal = 0,87.
Dalam contoh sumber daya, misalnya mesin diesel atau motor listrik, harus mampu
mengirimkan setidaknya 75 ÷ 0,87 = 86 [kW]. Motor hidrolik dan silinder bahwa persediaan
dengan pompa hidrolik juga memiliki efisiensi daya dan efisiensi sistem total (tanpa termasuk
penurunan tekanan dalam pipa-pipa dan katup hidrolik) akan berakhir pada approx. 0,75.
Cylinders biasanya memiliki efisiensi total sekitar 0,95 sementara motor piston hidrolik
aksial 0,87, sama seperti pompa. Secara umum daya yang hilang dalam transmisi energi
hidrolik dengan demikian sekitar 25% atau lebih di kisaran viskositas yang ideal 25-35 [cSt].
Perhitungan maks yang diperlukan. daya output untuk mesin diesel, estimasi kasar:
(1) Periksa maks. powerpoint, yaitu titik di mana tekanan aliran kali mencapai max. nilai.
(2) Ediesel = (Pmax · Qtot) ÷ η.
Qtot = menghitung dengan aliran pompa teoritis untuk konsumen tidak termasuk kebocoran
pada max. power point.
Pompa aktual Pmax = tekanan di max. power point.
Catatan: total η adalah efisiensi = (output daya mekanik ÷ input daya mekanik). Untuk
perkiraan kasar, η = 0,75. Tambahkan 10-20% (tergantung pada aplikasi) untuk nilai
(3) Hitunglah yang diperlukan diperlukan pumpdisplacement dari maks. jumlah aliran untuk
konsumen dalam kasus terburuk dan mesin diesel rpm di titik ini. The max. aliran bisa
berbeda dari aliran yang digunakan untuk perhitungan daya mesin diesel. Pompa rata-rata
efisiensi volumetrik, pompa piston: ηvol = 0,93.
Pumpdisplacement Vpump = Qtot ÷ ndiesel ÷ 0,93.
(4) Perhitungan prel. Kapasitas pendingin: Heat dissipation dari tangki minyak hidrolik,
katup, pipa dan komponen-komponen hidrolik kurang dari beberapa persen dalam ponsel
standar peralatan dan kapasitas pendingin harus menyertakan beberapa margin. Minimum
kapasitas pendingin, Ecooler = 0.25Ediesel
Sekurang-kurangnya 25% dari masukan kekuasaan harus disebarkan oleh pendingin ketika
puncak kekuasaan dimanfaatkan untuk waktu yang lama. Namun dalam kasus normal,
puncak kekuasaan digunakan hanya untuk periode singkat, sehingga diperlukan kapasitas
pendingin sebenarnya mungkin kurang. Volume minyak dalam tangki hidrolik juga bertindak
sebagai akumulator panas ketika puncak kekuasaan digunakan. Efisiensi sistem sangat
tergantung pada jenis peralatan alat kerja hidrolik, pompa hidrolik dan motor yang digunakan
dan input daya untuk sistem hidrolik dapat bervariasi banyak. Setiap rangkaian harus
dievaluasi dan siklus beban diperkirakan. Baru atau diubah sistem harus selalu diuji dalam
kerja praktis, yang mencakup semua kemungkinan beban siklus. Cara mudah untuk
mengukur rata-rata aktual daya yang hilang dalam sistem ini adalah untuk melengkapi mesin
dengan pendingin tes dan mengukur suhu pada pendingin minyak masuk, minyak pendingin
suhu di outlet dan aliran minyak melalui pendingin, ketika mesin dalam keadaan normal
modus operasi. Dari angka-angka ini uji disipasi daya pendingin dapat dihitung dan ini sama
dengan daya yang hilang ketika suhu stabil. Dari tes ini diperlukan pendingin yang
sebenarnya dapat dihitung untuk mencapai suhu minyak tertentu dalam tangki minyak. Satu
masalah dapat untuk merakit peralatan pengukuran inline, terutama aliran minyak meteran.