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27-449: The PTU is used when, for example, there is right hydraulic system pressure but no left hydraulic system pressure. In this example, the PTU transfers hydraulic power from the right hydraulic system to the left hydraulic system. A PTU consists of a hydraulic motor paired with a hydraulic pump via a shaft. As the connection is purely mechanical, there is no intermixing of hydraulic fluid between

54-460: A 'whoosh-whoosh' sudden spool up and spool down, which produces a loud noise that can be likened to a barking dog. Passengers who have flown on the Airbus A320 will frequently hear the PTU 'barking dog', generally when only one engine is running, or when the yellow system electric motorpump is the only active hydraulic power source; the PTU is mechanically activated in these cases. Consequently,

81-415: A Canadian patent was granted to Charles C. Barnes of Sackville, New Brunswick . There have been various improvements since, including a variable vane pump for gases (1909). One of the major advantages of the vane pump is that the design readily lends itself to become a variable-displacement pump, rather than a fixed-displacement pump such as a spur-gear or a gerotor pump. The centerline distance from

108-421: A PTU works is by surging, PTUs self-start by pure mechanical influence alone resulting from the delta-pressure between the two hydraulic systems it is connected to. Consequently, a PTU accelerates very rapidly under the delta-P induced load, and then stops just as suddenly once the pressure equalizes. Each pressure surge may only be a second long, causing a stop-start mode of operation. In practice, this results in

135-468: A canted internal swashplate to drive the piston shoes up and down around the internal piston slipway of the pump, lubricated by the fluid itself — this kind of PTU may appear to resemble two cylinders bolted together, with an inlet and outlet port at either end. An example of a straight axis in-line PTU can be found in the Cessna Citation X hydraulic system. A bent-axis in-line piston pump works

162-502: A circular rotor rotating inside a larger circular cavity. The centers of these two circles are offset, causing eccentricity. Vanes are mounted in slots cut into the rotor. The vanes are allowed a certain limited range of movement within these slots such that they can maintain contact with the wall of the cavity as the rotor rotates. The vanes may be encouraged to maintain such contact through means such as springs , gravity , or centrifugal force . A small amount of oil may be present within

189-502: A common type of vacuum pump , with two-stage pumps able to reach pressures well below 10 bar . These are found in such applications as providing braking assistance in large trucks and diesel-powered passenger cars (whose engines do not generate intake vacuum) through a braking booster , in most light aircraft to drive gyroscopic flight instruments , in evacuating refrigerant lines during installation of air conditioners , in laboratory freeze dryers, and vacuum experiments in physics . In

216-501: A description and an engraving of a rotary vane pump along with other types of rotary pumps, which suggests that the design was known at the time. In more recent times, vane pumps also show up in 19th-century patent records. In 1858, a US patent was granted to one W. Pierce for "a new and useful Improvement in Rotary Pumps", which acknowledged as prior art sliding blades "used in connection with an eccentric inner surface". In 1874,

243-454: A single hydraulic system on an airliner or business jet. Where an aircraft utility is powered by a single hydraulic system, PTUs become beneficial in allowing a single source of power, e.g. a pump powered by one surviving engine, to power more than one hydraulic system if the source of power in that system has failed. PTUs only work on the proviso that the system has not punctured and lost its fluid, because they do not permit fluid transfer, only

270-407: A surviving system may still provide sufficient power for critical systems to continue safe flight and landing. On airliners or business jets with powered flight controls, it is typical to have at least two hydraulic power control units (actuators) for each critical flight control surface — these are the elevators, rudder and ailerons. Only two sources might be used if some form of mechanical reversion

297-524: Is a type of positive-displacement pump that consists of vanes mounted to a rotor that rotates inside a cavity. In some cases, these vanes can have variable length and/or be tensioned to maintain contact with the walls as the pump rotates. This type of pump is considered less suitable than other vacuum pumps for high-viscosity and high-pressure fluids , and is complex to operate . They can endure short periods of dry operation, and are considered good for low-viscosity fluids . The simplest vane pump has

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324-547: Is in the trade-off. On the Airbus A320, the yellow system may power the green system, but because it is also bi-directional, if the starboard engine fails, the green system can help to power the yellow system by dumping excess power into it via the same mechanism. This is also known as a 'reversible' PTU. On some other aircraft, the direction of rotation of the PTU, and thereby the fluid flow through it, may be designed to work in only one direction. The Citation X business jet

351-517: Is one such aircraft with a uni-directional PTU, protected by check-valves and a back-pressure stall line, designed to allow the right hand hydraulic system to assist the left hand hydraulic system and the left hand auxiliary motorpump to retract the landing gear during a port engine failure only. On yet other aircraft, the function of a bi-directional reversible PTU can be accomplished with two uni-directional PTUs installed side-by-side arranged in opposite orientations to each other. The hydraulic system of

378-577: Is present (i.e. the pilot can still fly the aeroplane manually, but with some difficulty, via mechanical linkages and cables if hydraulic power is lost). On fly-by-wire aircraft, at least three independent power sources are needed. Spoilers and flaps meanwhile are considered secondary flight controls, and may only have a single hydraulic power source, providing the flight control can be deployed symmetrically. Likewise, landing gear, brakes and nosewheel steering are systems which are not considered critical for flight, and are subsequently typically only powered by

405-607: Is present. However, solenoid energized shut-off valves can isolate the PTU via a push-button switch (pb/sw) in the cockpit, but this feature is rarely used. Hydraulic fluid Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.133 via cp1102 cp1102, Varnish XID 572141023 Upstream caches: cp1102 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 07:50:03 GMT Rotary vane pump A rotary vane pump

432-596: The CH-47 Chinook helicopter uses twin uni-directional PTUs in this fashion. Hydraulic power transfer units are essentially nothing more than a hydraulic motor coupled to a hydraulic pump via a shaft; as such, they can conceptually be any kind of motor or pump such as a vane , gear , impeller or an in-line piston, or a variable displacement in-line piston pump. Commonly though, PTUs are paired in-line piston motors/pumps, in either bent or straight axis arrangements. A straight-axis in-line piston pump/motor relies on

459-419: The PTU is normally only heard on start-up or shut down. Very rarely is it heard in flight unless a momentary power deficit is present when retracting the gear, or a hydraulic fault has occurred. In Airbus literature, it is stated that the PTU 'self-tests', on startup, however the PTU does not contain any electronic motor assistance and cannot be commanded to start; it starts by itself only when hydraulic pressure

486-988: The atmosphere. On the discharge side of the pump, the vane chambers decrease in volume, compressing the fluid and thus forcing it out of the outlet. The action of the vanes pulls through the same volume of fluid with each rotation. Multi-stage rotary-vane vacuum pumps, which force the fluid through a series of two or more rotary-vane pump mechanisms to enhance the pressure, can attain vacuum pressures as low as 10 bar (0.1 Pa ). Vane pumps are commonly used as high-pressure hydraulic pumps and in automobiles, including supercharging , power-steering , air conditioning , and automatic-transmission pumps . Pumps for mid-range pressures include applications such as carbonators for fountain soft-drink dispensers and espresso coffee machines . Furthermore, vane pumps can be used in low-pressure gas applications such as secondary air injection for auto exhaust emission control, or in low-pressure chemical vapor deposition systems . Rotary-vane pumps are also

513-494: The green hydraulic system on an A320. (Modern A320s have the nosewheel steering powered by the yellow system.) The PTU solves this problem by allowing a rotary mechanical coupling between both systems, so the engine driven pump for the yellow (right hand) system on the starboard engine, which is oversized for normal hydraulic demand, can dump the excess power into the green system via the PTU, and allow powered landing gear retraction to continue, while maintaining hydraulic pressure to

540-450: The green system flight controls as well. Assuring landing gear retraction in a failure case is one potential assurance provided by a PTU. Alternatively, the designer may elect to have a second electric motorpump perform this role if a PTU is not desired. An additional motorpump may be heavier than a PTU however, and complex trade studies may favor one option or the other, depending on which failure cases are considered and how important weight

567-469: The inflow of gas into the pump becomes very low), a significant concern is contamination of the entire system by molecular oil backstreaming . Like many simple mechanisms, it is unclear when the rotary vane pump was invented. Agostino Ramelli 's 1588 book Le diverse et artificiose machine del capitano Agostino Ramelli ("The Various and Ingenious Machines of Captain Agostino Ramelli") contains

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594-418: The left and right hydraulic systems during PTU operation. Large transport category aircraft with hydraulically powered flight controls and utilities typically have multiple, independent hydraulic systems powered by a combination of engine-driven and electrically driven hydraulic pumps. Multiple hydraulic systems are typically needed for redundancy, where for instance if one system fails or loses hydraulic fluid,

621-427: The mechanism to help create a better seal between the tips of the vanes and the cavity's wall. The contact between the vanes and the cavity wall divides up the cavity into "vane chambers" that do the pumping work. On the suction side of the pump, the vane chambers are increased in volume and are thus filled with fluid forced in by the inlet vacuum pressure, which is the pressure from the system being pumped, sometimes just

648-450: The rotor to the eccentric ring is used to determine the pump's displacement. By allowing the eccentric ring to pivot or translate relative to the rotor, the displacement can be varied. It is even possible for a vane pump to pump in reverse if the eccentric ring moves far enough. However, performance cannot be optimized to pump in both directions. This can make for a very interesting hydraulic-control oil pump. A variable-displacement vane pump

675-540: The same way, but forgoes the canted swashplate; instead the whole rotating group is tilted to achieve the piston displacement. An example of a bent-axis in-line PTU can be found on the Hawker 4000 hydraulic system. In yet further representations, a bent-axis fixed-displacement motor/pump can be mated with a straight-axis variable displacement motorpump, as in the case of the Airbus A320 PTU. The mechanism by which

702-401: The transfer of mechanical work. For example, on the original design of the Airbus A320, the landing gear hydraulics (extension/retraction, brakes and steering) were solely powered from the green (left hand) system, powered by the left-hand engine driven pump. In the event of a port engine failure during take-off, the landing gear would not be able to retract as there is no auxiliary motorpump in

729-456: The vane pump, the pumped gas and the oil are mixed within the pump, and so they must be separated externally. Therefore, the inlet and the outlet have a large chamber, perhaps with swirl, where the oil drops fall out of the gas. Sometimes the inlet has louvers cooled by the room air (the pump is usually 40 K hotter) to condense cracked pumping oil and water, and let it drop back into the inlet. When these pumps are used in high-vacuum systems (where

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