Abstract: An aircraft auxiliary power unit is equipped with a charging compressor. A method determines a surge parameter indicative of a risk that the charging compressor will display the phenomenon known as surge. A method and a system control a relief valve of this charging compressor. The method for determining the surge parameter includes calculating this surge parameter Ppomp as being the sum of a first term T1 and of a second term T2, the first term T1 being calculated on the basis of a first pressure P1 measured downstream of a diffuser of the charging compressor, and of a second pressure P2 measured upstream of the diffuser, the second term T2 being calculated on the basis of a third pressure P3 measured upstream of the diffuser and of an ambient pressure Psamb indicative of a pressure of an ambient environment.

Abstract: A dry-type primary vacuum pump includes an injection device to distribute a purging gas in the pumping stages. The injection device includes: a first pressure sensor arranged on a common portion of the distributor, a second pressure sensor arranged on each branch of the distributor, and a control unit to generate a pulse width modulation command signal for the control of the regulation valves independently of one another as a function of the pressure measurement differences between the first pressure sensor and the second pressure sensors.

Abstract: An air compressor system includes a motor operably connected to an air compressor, a separator tank fluidly connected to the air compressor by a supply line, a compressed air line coupled to the separator tank, a service valve connected to the compressed air line and positioned downstream of the separator tank, and a controller in operable communication with the motor, wherein in response to the controller detecting the motor operating at an idle speed, the controller reduces the motor speed to a low idle speed and reduces pressure in the separator tank, the low idle speed being slower than the idle speed.

Abstract: A digital pressure switch is configured to be connected to a fluid pump. The digital pressure switch includes a pressure sensor configured to measure pressure inside a closed system, one or more relays configured to be connected to the fluid pump for activation and deactivation of the fluid pump, an amperage sensor configured to measure an amperage draw of an electric motor of the fluid pump, and a controller configured to process data from the pressure sensor and/or data from the amperage sensor and to activate or deactivate the motor of the fluid pump based on the data from the pressure sensor and/or the data from the amperage sensor, using the relays.

Abstract: A method of operating a relief valve assembly for an oil pump includes unblocking a first bypass inlet passage and blocking a first bypass outlet passage, a second bypass inlet passage, and a second bypass outlet passage with a plunger, introducing oil to the relief valve assembly, moving the plunger in a downward direction by a first displacement to unblock the first bypass outlet passage, starting a first bypass of the oil, moving the plunger in the downward direction by a second displacement to block the first bypass inlet passage and unblock the second bypass inlet passage, terminating the first bypass of the oil, moving the plunger in the downward direction by a third displacement to unblock the second bypass outlet passage, and starting a second bypass of the oil.

Abstract: An air system for use in an air bed system can include a manifold and one or more valves. The manifold can define an inlet, an outlet, and a vent fluidically connected to atmosphere. A method of operating an air bed system can include deflating an air chamber through the vent in a first valve configuration and through the vent and an exhaust port in a second valve configuration.

Abstract: Typical liquid-cooled compressors use the effective means of reducing no-load power by repeatedly starting and stopping an electric motor according to the amount of required air, but sufficient consideration has not been given to the fact that frequent starting and stopping of large-output electric motors leads to a decline in motor reliability. In order to solve this problem, a liquid-cooled compressor for circulating a liquid inside a compressor body using a pressure difference, and equipped with a cooling channel for circulating said liquid for cooling, configured so as to have an intake valve for adjusting the air intake of the compressor body, to change the amount of air taken in through the intake valve, and as a result, to perform a low-pressure operation during no-load operation at two levels of reduced operating pressure consisting of a value no less than a minimum circulation oil supply pressure and a low value.

Abstract: An air compressor system operably coupled to a power supply including an air storage tank and an air pump including an air manifold having an inlet configured to receive ambient air. The air pump is fluidly coupled to the air storage tank. The air compressor system also includes a motor having a first current level provided by the power supply to operate the air pump, a valve member in fluid communication with the inlet of the air manifold, and a controller operable to move the valve member to either increase or decrease a rate of ambient air traveling into the manifold. The controller monitors the first current level of the motor to change the rate of ambient air traveling into the manifold.

Abstract: A reciprocating compressor includes a cylinder block, a cylinder head, and a bypass unloader valve assembly. The cylinder block has a cylinder disposed therein. The cylinder head is secured to the cylinder block overlying the cylinder and has a suction plenum and a discharge plenum in selective fluid communication with the cylinder. The bypass unloader valve assembly is in operable communication with the cylinder head and is responsive to control signals to rapid cycle to allow for fluid communication of a refrigerant between the discharge plenum and the suction plenum.

Abstract: Provided is a dual pump system including: a dual pump provided with a plurality of chambers independent from each other, wherein an input and an output port are provided in each of the chambers; a plurality of output lines connected to the output ports of the plurality of chambers, respectively; and a switching valve that is provided in an output line of one side of the plurality of output lines, enables a fluid to flow to the output line when operating in one direction, and enables the fluid to be drained to an oil pan through a bypass line branched from the output line when operating in the other direction.

Abstract: Apparatus to treat an eye comprises an annular retention structure to couple to an anterior surface of the eye. The retention structure is coupled to a suction line to couple the retention structure to the eye with suction. A coupling sensor is coupled to the retention structure or the suction line to determine coupling of the retention structure to the eye. A fluid collecting container can be coupled to the retention structure to receive and collect liquid or viscous material from the retention structure. A fluid stop comprising a porous structure can be coupled to an outlet of the fluid collecting container to inhibit passage of the liquid or viscous material when the container has received an amount of the liquid or viscous material. The coupling sensor can be coupled upstream of the porous structure to provide a rapid measurement of the coupling of the retention structure to the eye.

Abstract: A method for operating a compressor including providing suction pressure measurement, final pressure measurement, throughput measurement is provided. Using a first control characteristic map a target value for a pump surge limiter is determined from one or two of the measurements, and the pump surge limiter compares the target value to the throughput measurement, wherein the pump surge limiter opens a bypass valve when the measured value falls below or exceeds the target value, such that the final pressure is lowered or the flow through the compressor is increased. In the event of failure of a measurement, a further measurement of another physical variable of the compression process, together with a measured variable that did not fail or a modification of the measured variable, is an input variable for a substitute control characteristic map, form which a substitute target value is determined.

Abstract: A compressor assembly (10) has a fluid inlet positioned to facilitate the passage of a fluid. The compressor assembly includes a compressor housing (60) defining a compressor inlet (35), a compressor rotating element (45) rotatably supported at least partially within the compressor housing, and an inlet guide vane assembly (500) including a housing (505) that defines a flow passage (525), a plurality of vanes (540), and a guide ring (555). Each of the plurality of vanes is rotatably supported by the housing and is coupled to the guide ring such that each of the vanes is rotatable simultaneously between a first position and a second position to control the quantity of fluid that passes through the flow passage to the compressor rotating element.

Abstract: A single piston fuel pump comprising a pump housing a pump inlet and an outlet. The pump housing mounts a proportional solenoid operated inlet metering valve with variable orifice, an inlet check valve, a pumping chamber, a pumping piston, an outlet check valve, and a pressure relief valve, wherein the inlet metering valve, the inlet check valve, the outlet check valve, and the pressure relief valve are all mounted on a common axis.

Abstract: Systems and methods for sensing bubbles during fluid infusion are disclosed. An infusion device comprises a pathway, at least one pump adjacent the pathway, first and second bubble sensors positioned adjacent the pathway, and a processor. The pathway is adapted to receive tubing. The pump alters the pathway to pump fluid through the tubing when the tubing is received in the pathway. The second bubble sensor is spaced from the first bubble sensor. The first and second bubble sensors are configured to detect a bubble in the fluid being pumped through the tubing. The processor is programmed to determine that the first bubble sensor detects a bubble, determine whether the second bubble sensor detects a bubble, and to generate an alarm condition only when the first bubble sensor and the second bubble sensor detect the same bubble.

Abstract: An electric compressor 10 includes a compression mechanism 11, an electric motor 12 driving the compression mechanism 11, and a control portion 13 controlling to drive the electric motor 12, incorporated into a single casing, and further includes a temperature detector 14 detecting a temperature of one or more components constituting one or both of the control portion 13 and the electric motor 12, and a current detector 15 detecting a current flowing through the component. When the temperature detected by the temperature detector 14 is a temperature Td, the current detected by the current detector 15 is a current Id, and a current corresponding to the temperature Td at a temperature characteristic relating to the current specific to the component is a current Ia(Td), the control portion 13 stops driving the electric motor 12 on the basis of a result of comparison between Ia(Td) and Id.

Abstract: A system includes a detector configured to detect a fog condition within an air flow directed toward a compressor. The system also includes a controller coupled to the detector, wherein the controller is configured to activate a first control measure in response to the fog condition.

Abstract: A pump for pumping fluid includes a tube platen, a plunger, a bias member, inlet and outlet valves, an actuator mechanism, a position sensor, and a processor. The plunger is configured for actuation toward and away from the infusion-tube when the tube platen is disposed opposite to the plunger. The tube platen can hold an intravenous infusion tube. The bias member is configured to urge the plunger toward the tube platen.

Abstract: A control system for a pumping apparatus consisting of an engine-driven primary pump includes an intake pressure regulating system for maintaining the intake pressure above a preset low value, a discharge pressure regulating system for maintaining the discharge pressure below a preset maximum value, and a master controller for monitoring, recording, and controlling the intake and discharge pressure regulating systems and other components of the system. The discharge pressure regulating system includes a pump governor which varies the engine RPM and operates a relief valve in response to fluctuations in discharge pressure. The intake pressure regulating system includes a reserve tank that is automatically maintained at a preset level which determines the minimum intake pressure of the system. The system may also include a priming pump, foam tanks, foam pumps, bottled nonflammable gas, and an air compressor.

Abstract: In a method and device for controlling a hydraulic drive system, in particular in a crane or construction machine, a closed hydraulic circuit has a hydraulic pump and motor in which depending upon a desired value (ndes) of an output parameter of the hydraulic circuit, an actuating signal (I) is generated for adjusting the hydraulic pump and/or motor. The actuating signal (I) is limited and/or reduced by a superordinate control module (6) depending on matching of a specified power value (P+; P?) with a current power value (PPu; PM) of the hydraulic pump and/or motor.

Abstract: A peristaltic pump is able to deliver accurate volumes over the life of a pump set that is operated on by the pump to drive the flow of fluid. The pump delivers fluid in small volumes or aliquots. In order to deliver fluid at any particular selected flow rate, the pump determines how often the rotor will rotate. The pump is able to calculate aliquot volume based on selected flow rate, but also on a factor that compensates for changes in the dimensions of the pump set over its life.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate a pump to obtain a formation fluid sample from a formation adjacent to a wellbore disposed within a reservoir, to detect a phase behavior associated with the fluid sample, and to adjust the volumetric pumping rate of the pump while repeating the operating and the detecting to maintain the pumping rate at a maintained rate, above which the phase behavior changes from a substantially single phase fluid flow to a substantially multi-phase flow. Additional apparatus, systems, and methods are disclosed.

Abstract: Device to prevent the formation of condensate in compressed gas coming from an oil-injected compressor element which is connected to an oil separator which is connected to the compressor element by an injection pipe, and wherein a cooler is provided in the injection pipe which can be bridged by means of a bypass. A controlled mixing valve is connected to the injection pipe and to the bypass, and a control device controls the mixing valve to adjust the compressed air temperature by adjusting the flow distribution through the mixing valve.

Abstract: A method of operating a compressor of a compressor system uses three models. Each model of the three models describes a surge line of the compressor as a function of any two of three operating parameters of the compressor. The three operating parameters include head (H), flow (Q), and speed (N). The method includes measuring operating characteristics of the compressor system using sensors, and determining a current value of the three operating parameters based on at least some of the measured operating characteristics. The method also includes locating operating points of the compressor on each of the three models based on the current value of the operating parameters, and identifying a sensor fault that affects the determination of at least one of the operating parameters. The method further includes avoiding surge of the compressor using one model of the three models. The one model being a model that is a function of two operating parameters unaffected by the sensor fault.

Abstract: A method of inhibiting combustion within a vacuum pump is provided. The method steps include monitoring and composition of a fluid within the pump and supplying purge gas to the pump to inhibit the onset of a combustion of the fluid. There is also provided a pumping arrangement comprising a vacuum pump (1) together with means (8) for supplying purge gas to the pump. Sensor means (21a, 21b, 21c) are provided for outputting a signal indicative of the onset of a combustion condition within the pump. Control means (22) receive the signal and, in turn, actuate the supply means (9) dependant on the signal received.

Abstract: To regenerate a compressed air supply device of a commercial vehicle, a first compressed air circuit is supplied with compressed air until reaches a predetermined target pressure value; then a second compressed air circuit is supplied. Between these steps, the method: (1) regenerates an air dryer when the pressure in the first compressed air circuit has reached the target pressure value, and when a moisture value of the air dryer exceeds a predetermined target moisture value; (2) terminates the regeneration when the pressure has dropped to a predetermined limit pressure value or the moisture value of the air dryer has reached or dropped below the target moisture value; (3) supplies the first compressed air circuit until it has reached the predetermined target pressure value; and (4) repeats the preceding intermediate steps when the moisture value is greater than the target moisture value.

Abstract: To detect a failure of a compressed air consumer circuit in a compressed air system for vehicles, pressure is continuously measured in compressed air consumer circuits and evaluated in an electronic control unit which compares the pressure values and/or determined negative pressure gradients of the compressed air consumer circuits with a respective threshold value and shuts off an air-consumer circuit if the pressure values and/or negative pressure gradients thereof satisfy a circuit-failure criterion. The circuit-failure criterion is satisfied when the pressure values and/or pressure gradients are below the respective threshold value for a time equal to or longer than the time of a dynamic pressure change or of a dynamic pressure collapse.

Abstract: A compressor apparatus (20) has a housing (22) having first (53) and second (58) ports along a flow path. One or more working elements (26; 28) cooperate with the housing (22) to define a compression path between suction (60) and discharge (62) locations along the flow path. An unloading valve (100) has a valve element (102) having a range between a first condition and a second condition, the second condition being unloaded relative to the first condition. Means (120, 160) bias the valve element toward a third condition intermediate the first and second conditions.

Abstract: An oil supplying apparatus includes a first oil path supplying working oil from an outlet port to a portion to be supplied with the working oil, a second oil path supplying the working oil to an oil pressure control valve, a relief oil path, and a valve body oil path. Depending on first, second, third, and fourth ranges of the oil pressure of the working oil in the first oil path, the working oil is supplied to the first oil path, is supplied to the first oil path and to the relief oil path via the valve body oil path, is directly supplied to the first oil path and is supplied to merge into the first oil path via the oil pressure control valve, and is supplied to the first oil path and to the relief oil path via the oil pressure control valve respectively.

Abstract: A compressor (20) has an unloading slide valve (100). The valve has a valve element (102) having a range between a first condition and a second condition, the second condition being unloaded relative to the first condition. A first surface (200) of the valve element (102) is in sliding engagement with a second surface (202) of the housing (22) during movement between the first and second conditions. The compressor includes means for lubricating the first (200) and second (202) surfaces.

Abstract: A system and method for compensating a calculated or flow rate of fuel dispensed to a vehicle via a fuel flow path in response to a determination of a non-steady state condition based on data corresponding to a signal transmitted by a pressure sensor operatively coupled to the fuel flow path and configured to sense pressure therein, where the pressure sensor is adapted to transmit a signal representative of the sensed pressure.

Abstract: A method of operating a compressor of a compressor system is disclosed. The method uses three models. Each model of the three models describes a surge line of the compressor as a function of any two of three operating parameters of the compressor. The three operating parameters include head H, flow Q, and speed N. The method includes measuring operating characteristics of the compressor system using sensors, and determining a current value of the three operating parameters based on at least some of the measured operating characteristics. The method also includes locating operating points of the compressor on each of the three models based on the current value of the operating parameters, and identifying a sensor fault that affects the determination of at least one of the operating parameters. The method further includes avoiding surge of the compressor using one model of the three models. The one model being a model that is a function of two operating parameters unaffected by the sensor fault.

Abstract: An oil supplying apparatus includes a first oil path supplying working oil from an outlet port to a portion to be supplied with the working oil, a second oil path supplying the working oil to an oil pressure control valve, a relief oil path, and a valve body oil path. Depending on first, second, third, and fourth ranges of the oil pressure of the working oil in the first oil path, the working oil is supplied to the first oil path, is supplied to the first oil path and to the relief oil path via the valve body oil path, is directly supplied to the first oil path and is supplied to merge into the first oil path via the oil pressure control valve, and is supplied to the first oil path and to the relief oil path via the oil pressure control valve respectively.

Abstract: A digit button-operated air compressor output control structure for controlling output of compressed air from an air compressor by means of a digital control panel and an air pressure regulating structure with internal pressure sensors for enabling the user to set the desired output air pressure quickly and to control the output air pressure stably.

Abstract: A multiple configuration air mattress pump system is disclosed. The pump system includes a number of standard components with a few inexpensive varied components to allow for easy and less expensive use of the pump with mattresses having varying numbers of inflatable zones.

Abstract: The present invention relates to a control system for protection against breakage of the lubricating-oil film in the bearings of hermetic compressors, as well as to a control method that has the objective of guaranteeing that a variable-capacity compressor should be maintained above a minimum rotation in order to prevent the oil film close to the respective bearing from breaking. One of the forms of achieving the objectives of the present invention is by means of a control system for protection against break of the lubricating-oil film in bearings of hermetic compressors, a microprocessor (10) actuating a set of switches (SW2M) selectively, so as to generate a rotation at the motor-compressor assembly (20, 21), the compressor (21) having a minimum rotation (RPMmin) of the compressor (21) so that the oil film will not be broken.

Abstract: The invention relates to valves for air compressors, and more particularly, to an unloading/venting valve having integrated therewith a high-pressure protection valve where a pressure reducing valve has a discharge port in communication with the air system and a vent. The valve utilizes a valve body biased to form a seal between the discharge port and the vent. A governor monitors the air pressure in the system and generates a signal to move the valve body against the bias and unloads the system when a first predetermined threshold pressure is reached. In the event of a failure of the valve body to move at the first threshold pressure, the valve body is movable against the bias in response to a second predetermined threshold pressure reached in the system, thereby unloading the system.

Abstract: A screw compressor is equipped with a manually operated internal volume ratio adjusting slide valve and capacity adjusting slide valve. The compressor is simple in construction, can be produced with low cost, can accommodate decrease in suction pressure, for example, in an aged gas well, and can be operated without an electric power source for controlling the operation thereof. Also a combined screw compressor unit consisting of a plurality of screw compressors for producing high discharge pressure is provided which can accommodate high suction pressure in order not to overload the higher pressure compressor or compressors with the efficiency of the unit kept as high as possible by including at least a screw compressor according to the present invention in the unit.

Abstract: A system and method of surge limit control for turbo compressors including a turbo compressor having an inlet and an outlet, an anti-surge valve, a variable speed drive to operate the compressor, a rotational speed transmitter, an inlet temperature transmitter, an inlet pressure transmitter, an outlet pressure transmitter and/or guide vanes, and a controller, the controller including a PID control module wherein the computer uses information from the transmitters to continuously calculate a pressure ratio of the compressor at the compressor's current operational speed and compare it to the compressor's calculated pressure ratio at surge limit conditions. A computer generates a control signal for determining when to open the anti-surge valve if the pressure ratio of the compressor at the compressor's current operational speed guide vanes are within a user defined safety margin to the calculated pressure ratio at surge limit conditions.

Abstract: A multi-stage screw compressor unit and method of operation thereof are provided, which enable operation with high efficiency always even when suction or discharge pressure fluctuates widely, the compressor unit comprising a combination of a compression stage provided with an unloader slide valve and that provided with an internal volume ratio control valve, or a combination of compression stage provided with an internal volume control valve and that of fixed internal volume ratio, or a combination of compression stages each provided with an internal volume control valve.

Abstract: Blood component processing systems and methods are coupled to a blood component processing device. The systems and methods include a fluid circuit that comprises at least one fluid pressure actuated pump station, at least one fluid flow path communicating with the pump station, and at least one valve in the fluid flow path. A control module is sized and configured to interact with the fluid circuit. The control module includes an actuator to selectively apply fluid pressure to the pump station in concert with operation of the valve to pump fluid through the fluid flow path in response to a control program. A controller coupled to the control module includes the control program and a fluid circuit integrity test function.

Abstract: A compressed air treatment device is designed to be installed in an industrial vehicle consisting of a motor vehicle that can pull a trailer. The device comprises: an inlet for air from a compressed air source; at least one air outlet which is connected to a tank that is intended to supply the service braking system; a set of electropneumatic components for distributing the compressed air which comes from the compressed air source and which is intended for the tank(s); an electronic control unit which can control said set of electropneumatic components, the control unit being connected to a computer communication bus and to various electrical components such as sensors or switches.

Abstract: Blood component processing systems and methods are adapted to be coupled to a blood component processing device. The systems and methods employ a fluid circuit comprising at least one fluid pressure actuated pump station, at least one fluid flow path communicating with the pump station, and at least one valve in the fluid flow path. A control module sized and configured to interact with the fluid circuit includes an actuator to selectively apply fluid pressure to the pump station in concert with operation of the valve to pump fluid through the fluid flow path in response to a control program. A circuit board assembly is associated with the actuator in electrical conductive interaction with fluid in the pump station. The circuit board assembly comprises a part of a capacitive sensing circuit. The circuit board assembly can comprise, e.g., a printed circuit board assembly, or a flexible circuit, or a molded circuit. The circuit board assembly can, e.g.

Abstract: The invention provides a method of operating a screw compressor equipment without reducing the efficiency, in which a screw compressor 1 of which the internal volume ratio is variable by means of an internal volume ratio control valve is driven by a driving machine 2, the discharge side of the compressor 1 is communicated with the suction side of the same by way of a bypass control valve 9 as needed, the internal volume ratio control valve 3 is always controlled to be located at a position calculated so that the internal volume ratio with which the polytropic efficiency is maximum is obtained, and gas flow rate is controlled by controlling the rotation speed under normal conditions and controlled by controlling the bypassing flow rate from the discharge side to the suction side under very low rotation speed.

Abstract: To protect a turbocompressor (3) with a downstream process from operation in the unstable working range, a machine controller is used, which optionally contains—besides a surge limit controller (15)—an intake pressure controller (11), an end pressure controller (20) and a bypass controller (9). A control matrix is determined from the position of a control unit (fuel gas control valve 6) determining the flow to the process, optionally taking into account additional influencing variables such as the compressor intake pressure and the compressor discharge pressure.

Abstract: In a turbo-molecular pump, a rotor is supported by a magnetic bearing (3) in a non-contact mode. A pump control section (2) has a magnetic bearing control device (8) with a digital signal operating processor or DSP (7) which is programmable by a software or which can execute a programmed software. The digital signal operating processor (7) performs the control of a heating system, namely, a heater, as well as the control of the magnetic bearing (3).

Abstract: A compressor protection and control subsystem for a rotary compressor provides temperature pressure, mis-wiring and vibrational protection for the scroll machine. The vibrational protection comprises a vibration sensor which is integrated on the circuit board of the protection and control subsystem. The vibration sensor, in conjunction with at least one timer, monitors the vibrations of the scroll machine and will shut down the machine when excess vibrations are sensed over a prespecified period of time. The temperature system monitors operating temperature conditions the pressure system monitors operating pressures and the mis-wiring system monitors the power supplied to the compressor. Once an undesirable characteristic is identified, the operation of the scroll machine is stopped. These protection systems are integrated into a single subsystem which identifies the reason of shutting off the scroll machine in order to simplify repairs needed.

Abstract: In a turbo-molecular pump, a rotor is supported by a magnetic bearing (3) in a non-contact mode. A pump control section (2) has a magnetic bearing control device (8) with a digital signal operating processor or DSP (7) which is programmable by a software or which can execute a programmed software. The digital signal operating processor (7) performs the control of a heating system, namely, a heater, as well as the control of the magnetic bearing (3).

Abstract: A compressor, especially for compressing the fuel gas for a gas turbine, is controlled by a throttling member (9) arranged on the intake side of the compressor as a function of the gas consumption of the user (7) such that the flow cross section is reduced during a reduction in gas consumption. The intake-side throttling member may be additionally controlled as a function of the pressure on the intake side of the compressor. Additional control circuits, especially an end pressure controller (19), which maintains the end pressure by acting on the guide vanes or on the speed of rotation of the compressor, and/or a pump surge limiter (33), which acts on a blow-by valve (29) connecting the outlet side to the intake side of the compressor (3), may be additionally present.

Abstract: The rated system pressure in a pressure control system is adjusted through a pressure relief valve (2). In addition to the pressure relief valve (2), the system includes a check valve (4), a pressure sensor (3), a position switch (10), a first pressure adjustment member (13) for the relief valve, a second pressure adjustment member (12) for the check valve (4), an actuator (16), and a microcontroller (15) with a memory (6) and a display (7). Faults caused by pressure adjustment interactions are prevented by permitting an adjustment of the pressure relief valve only if the check valve is fully open and a pump provides pressure. For this purpose the actuator (16) of the check valve in its normal position prevents an adjustment of the pressure relief valve. Opening the check valve by the actuator permits adjusting the pressure relief valve (2) and the switch (10) operated through the actuator sends a signal to the microcontroller to drive the pump.