Piston machines are fluid energy machines with a working space , the volume of which is intermittently changed by a usually periodically moving displacer ( piston ) . The fluid flow and pressure differences between inlet and outlet are variable in piston machines due to the intermittent mode of operation , which distinguishes them from continuously operating flow machines such as gas turbines , in which the fluid flow and pressure curve remain stationary .
In general, it can be both working machines (from the point of view of hydraulics : "transmitter" ), as well as power machines (motors; in hydraulics: "slave" ), with some piston machines also being able to work reversibly in both directions, such as hydraulic cylinders as well as some hydraulic pumps that work in reverse as a hydraulic motor or a Stirling motor that is driven as a work machine to become a heat pump . There are two different kinematic principles:
- Reciprocating piston machines in which the displacer is a piston that moves back and forth in a cylinder . In the broadest sense , machines that work with a diaphragm ( diaphragm pump , diaphragm cylinder ) are also piston machines.
- Rotary piston machines in which specially shaped displacers either only rotate or also revolve on a circular path.
In reciprocating piston engines which is the displacer , a more or less disc-shaped piston (engl. Piston ) extending in a cylinder reciprocates or a cylindrical plunger , which, for example, in a stuffing box is running. There are reciprocating piston machines both as work machines ( pump = transmitter ) and as prime movers ( slave ) that drive a load, such as a hydraulic cylinder . Similar principles apply in pneumatics , but the compressibility of the working gas with compression and expansion must then also be taken into account. A distinction must be made depending on the type of kinematics :
- Simple reciprocating piston machines that act directly with their linear movement via a push rod , such as simple pneumatic cylinders , hydraulic cylinders or a plunger pump :
- Reciprocating piston engines with crank mechanism in which the linear movement kinematically via a thrust crank in a rotational movement is implemented as reciprocating pumps and compressors ( compressor ) as a working machine , as well as reciprocating engines as the engine :
- Aviation piston machines, on the other hand, transfer the linear movement via a rack to a shaft ( rack and pinion drive ), like the aviation piston engine :
- Free-piston machines , in which the piston itselfacts directly with its linear movement, are usually free-piston motors such as explosion rams or free-piston linear generators or combined with a turbine such as the Pescara gas generator, in which a free-piston diesel engine works against gas springs and its exhaust gases are used in a turbine as a prime mover become
Rotary piston machines
- Rotary lobe machines with direct rotary movement of the piston are rotary lobe pumps , such as rotary vane pumps , gear pumps or Roots blowers , which conversely can also work as hydraulic motors : The rotary lobe pumps also include the liquid ring pumps .
- Rotary piston machines , especially rotary piston pumps or rotary piston engines with special kinematics such as the Wankel engine , which works as a periodically working fluid energy machine with a variable pressure curve with a rotating and rotating piston:
|Rotary piston machines||DKM||-||-||Roots blower|
|Rotary piston machines||KKM||+||-||Rotary engine|
|Rotary piston- type rotary piston machines||DUKM||-||+|
|Rotary piston-type rotary piston machines||KUKM||+||+||Vane pump|
With DUKM and KUKM, the speeds are usually limited if the inertia forces cannot be balanced.
|Machine type||Working machines||Power machines|
|Hydraulic piston machines
(≈ incompressible media)
|Piston pumps||Hydraulic motors|
|Thermal piston machines
Internal combustion engine,
engine, steam engine, Stirling engine
- Displacement machine
- Free piston machine
- Rotary piston pump
- Working machine
- Power machine
- Cylinder pressure indexing
- Wolfgang Kalide: Pistons and flow machines. 1st edition, Carl Hanser Verlag, Munich Vienna, 1974, ISBN 3-446-11752-0
- DIN 1940 standard "Combustion Engines", various editions since July 1946