Abstract: A brake control valve arrangement includes an electro-pneumatic brake control valve block having a hold valve and a vent valve, a main regulator valve and an emergency and a tare pressure regulator. The valve block has an inlet for a brake supply pressure and an outlet for a brake cylinder, wherein an inlet and a vent pneumatic opening is provided for the hold valve and vent valve. The arrangement also includes a configuration module in pneumatic connection with the brake supply pressure and providing a pneumatic path to the inlet, and a pneumatic path to the vent valve from the brake cylinder, the arrangement also including at least one choke configured to control air flow in pneumatic paths to the inlet opening and vent opening.

Abstract: A normally closed port valve seals a hydraulic hose connection port of a hydraulic bicycle component. Connection of an end of a hydraulic hose assembly to the port opens the valve, placing the assembly's hydraulic fluid chamber in fluid communication with the interior of the hose assembly. A hydraulic cylinder of the assembly is in fluid communication with the chamber. A spring may be used to bias the valve to a closed condition and simultaneously to bias a brake actuating piston to a non-actuated position.

Abstract: A brake device is provided with an actuator which is operated by a pressure medium, used to apply and release a vehicle brake, especially a brake of a rail vehicle, includes an actuating piston which defines two pressure chambers. One pressure chamber impinges upon the vehicle brake in an applied position and the other pressure chamber impinges upon the vehicle brake in a release position. The two pressure chambers are connected to each other by a line with an overflow valve which opens at least during part of the transition phases—between the release position and open position—and which is otherwise closed.

Abstract: A service portion of a rail pneumatic brake control valve which includes a piston responsive to pressure differential between brake pipe pressure at a brake pipe port and reservoir pressure at a reservoir port and a first valve controlled by the piston to determine pressure in a brake cylinder for a service application. A stability choke and check valve are connected in series between the brake pipe port and the reservoir port. The check valve permits flow from the brake pipe port to the reservoir port and prevents flow from the reservoir port to the brake pipe port independent of the piston.

Abstract: An interface system including locomotive and car electrical trainline terminals, locomotive and car brake pipe ports and a locomotive pressure supply port. A train brake pipe valve controls pressure on the train brake pipe port. A controller monitors pressure on the locomotive brake pipe port and controls the train brake pipe valve in response to pressure on the locomotive brake pipe port. The controller also provides ECP commands on the train electrical terminal in response to pressure on the locomotive brake pipe port and provides electrical power on the train terminal from the locomotive electrical trainline terminal. The car electrical terminal is connected to the ECP trainline for providing ECP commands and power to the ECP equipped train devices. The controller may also control an emergency valve to produce an emergency on the locomotive brake pipe port. A transition valve on the brake pipe port allows bi-directional connection of the interface system.

Abstract: A pneumatic control system for a freight car having a brake pipe, auxiliary and emergency reservoirs normally charged with pressurized fluid from the brake pipe, a fluid pressure activated brake cylinder device and an exhaust including an electronic controller, at least one pressure sensor, an electrically operated supply valve controlled by the electronic controller selectively communicating the brake cylinder with one of the reservoirs to perform a brake application, an exhaust valve selectively communicating the brake cylinder with the atmosphere thereby performing a brake release function, and an electronically operated exhaust latching valve controlled by the electronic controller to selectively signal the exhaust valve to connect the brake cylinder to the exhaust.

Abstract: The invention relates to a pneumatic brake force producing device comprising at least one suction device for the surrounding air. The aim of the invention is to prevent the condensation of air humidity in the brake force producing device. According to the invention, this can be achieved in an especially reliable manner by passing the aspirated air through a condenser before it enters the brake force producing device. The air-guiding parts in said condenser are at a lower temperature than the air-guiding parts of the brake force producing device in such a way that enough air humidity from the air condenses in the condenser to avoid further condensation in the brake force producing device.

Abstract: The method includes reducing pressure of a charged brake pipe to a predetermined pressure value. The brake pipe is then charged only from the head end unit. Each intermediate brake pipe monitoring and charging device sequentially reports on the network a pressure which is an increase if the brake pipe is continuous between it and the head end unit. Subsequent to receipt of a report of an increased pressure on the network from an intermediate unit, the head end unit commands that intermediate unit to participate in charging the brake pipe. The head end unit determines the brake pipe continuity from the pressure increases reported by the intermediate units.

Abstract: A brake fluid reservoir (10) for a vehicle hydraulic brake system has a filler neck (16), a lid (18) which closes the filler neck, and a device for pressure compensation between the reservoir interior and the ambient atmosphere. In order, when the brake fluid reservoir (10) is in a steeply inclined position, to prevent an escape of brake fluid, in the lid (18) a first brake fluid forced-flow channel (32) is formed, which has an inlet (34) at the inside of the lid and an outlet (36) towards the outside of the lid. The forced-flow channel (32) extends between the inlet (34) and the outlet (36) along a curved path, which in relation to a plan view of the lid (18) runs through at least two quadrants.

Abstract: A method for providing brake control for a rail car having a brake cylinder, a reservoir, and an exhaust vent includes steps of fluidly interconnecting four electrically controlled valves between a train brake pipe, the brake cylinder, the reservoir, and the exhaust vent, and controlling air flow between the brake pipe, car brake cylinder, car reservoir, and exhaust vent using the valves. The above described method allows mixing of conventional ABDW rail cars with ECP-equipped cars in an ECP-equipped train.

Abstract: An integrated pneumatic and electropneumatic train brake system and method of operation. An electropneumatic brake controller in at least one of the locomotives provides an emergency brake signal on a brake pipe and the network to the pneumatic and electropneumatic brakes for an emergency position of the operator interface. The brake controller also provides an emergency signal only on the network to the electropneumatic brakes in the continuous service position of the operator interface.

Abstract: A single car tester including a housing having a hanger to mount the housing to a car coupler or ladder of the car. Various configurations of valves and sensors are described to perform a single car test. The controller includes a program for uniquely performing the required tests.

Abstract: A single car tester including a housing having a hanger to mount the housing to a car coupler or ladder of the car. Various configurations of valves and sensors are described to perform a single car test. The controller includes a program for uniquely performing the required tests.

Abstract: A vent valve made from a standard emergency brake valve portion. It includes an emergency portion body with an interface to be mated with the emergency portion interface of the pipe bracket. The body includes a casting with at least one cover and the casting including all the cast cavities and passages for an emergency portion. A vent valve selectively connects a first brake pipe port to a vent port on the body, A vent piston controls the vent valve and a discharge valve pneumatically controls the vent piston. An emergency piston is responsive to brake pipe pressure for controlling the discharge valve. The body does not include at least one of an in shot valve and an accelerated application valve.

Abstract: A test connector adapter plate for use with a pipe bracket portion of a freight brake control valve of a railway freight vehicle and with a portable automated single car brake tester. The pipe bracket portion having four test ports vertically disposed on a front side of such pipe bracket portion for single car brake testing. These test ports are fluidly connected to passageways within the pipe bracket for communicating fluid pressure with brake pipe, brake cylinder, emergency reservoir and auxiliary reservoir, respectively. A first member of the test connector adapter plate is engagable with the test ports on such front side of the pipe bracket portion for accessing the passageways respectively communicating to brake pipe, brake cylinder, emergency reservoir and auxiliary reservoir and are fluidly connected to respective passageways within the adapter plate.

Abstract: A braking system is able to meet emergency stopping distance requirements associated with a failed rear axle service control line by modifying the service relay valve. The service relay valve incorporates a biased double check valve so that an additional or secondary control line from the foot control valve communicates with the service port of the relay valve. If the primary circuit is operational, a biasing force imposed on the double check valve permits normal operation via the primary service line. On the other hand, if the primary service line is lost, the biasing force is overcome and communication between the secondary service line and the service port of the relay valve is established.

Abstract: A wafer flange assembly designed to fit in between existing components of a freight car air braking system comprises a wafer flange having a center bore and an O-ring in surrounding relation thereto to create an airtight flowpath between the air braking system components, and further comprises a tunnel bore disposed within the wafer flange and creating an airtight flowpath from the brake cylinder line to a male quick disconnect valve mounted to the wafer flange, whereto a female quick disconnect valve may be attached to facilitate measurement of the brake cylinder line air pressure.

Abstract: Air braking system of vehicles usually have a piston compressor (C) and a desiccant (D) for drying the compressor output air. The desiccant is periodically regenerated by downstream air from e.g. a reservoir (R). When a compressor is brought on load, the initial charge of air may be oil laden. The invention provides a delay mechanism to permit such initial charge of air to pass directly to exhaust.

Abstract: A locomotive brake control system including train brake and bail-off with hold and/or blending features. A preliminary brake cylinder pressure control signal is provided to the propulsion system which provides a blending signal as a function of the preliminary brake control signal and dynamic braking. Holding and blending reservoirs are computer simulated.

Abstract: A brake pipe control apparatus of the type that defines primary and control passage networks has been improved. The primary passage network interconnects the brake pipe to at least one pneumatic valve in the apparatus. The control passage network interconnects a source of control pressure to at least one magnet valve used to cause operation of the pneumatic valve(s). The improvement includes first and second check valves and a passageway added between the two passage networks. The first check valve is incorporated into the control passage network between an inlet channel thereof that connects to the source and a branched channel thereof that connects to the magnet valve(s). The first check valve is situated to prevent air from flowing to the source from the branched channel when pressure in the source is low relative to pressure in the branched channel. The passageway interconnects the branched channel and the primary passage network.

Abstract: An adaptor for connecting brake pipe, brake cylinder, emergency and auxiliary reservoir ports on a standard pipe bracket to an electropneumatic control valve. The adaptor also includes threaded post to mount the electropneumatic valve to the adaptor and fastener apertures to receive fasteners to mount the adaptor to the pipe bracket.

Abstract: In a locomotive braking system, an independent brake control circuit uses second control signal(s) to adjust pressure in a first reservoir. A microprocessor derives the second control signal(s) based on at least a first control signal indicative of brake handle position and first feedback indicative of first reservoir pressure. One pneumatic relay adjusts pressure in a 20 pipe based on first reservoir pressure. An automatic brake control circuit uses third control signal(s) to adjust pressure in a second reservoir. The microprocessor derives the third control signal(s) based on at least second feedback indicative of second reservoir pressure and third feedback indicative of pressure in a 20 pipe. Another pneumatic relay controls pressure in a brake cylinder based on whichever of at least the 20 pipe and the second reservoir delivers a highest pressure. A new system for backup control of the 20 pipe includes the microprocessor and a timer.

Abstract: In a microprocessor-controlled electro-pneumatic brake control system for a railway train, pressure in the brake cylinder is maintained despite the loss of pressure in the "20 pipe" brake line, or failure of a key relay valve that controls pressure to that brake line. Feedback signals derived from the "20 pipe" brake line when found to be inappropriate after a predetermined amount of time are substituted for by brake command signals generated by the brake controller.

Abstract: A brake pipe leakage test for a train is performed using an improved brake pipe drop pressure method prior to departure of the train consist from a railyard terminal. The train consist includes a brake, a brake pipe, and a brake pipe cutoff valve.

Abstract: An automated terminal test system performs a terminal test of brake equipment on a train. The system includes a test control box connected to a head of train locomotive and accessible from outside of such locomotive. Linked to such brake equipment, the test control box has a control for activating the test control box, applying and releasing the brakes, and charging and venting such brake pipe. The system also includes an end of train transceiver device connected to such brake pipe on a last railcar of such train. The end of train transceiver device monitors pressure within such brake pipe on such last railcar, senses movement of such last railcar, and communicates signals representative of such pressure monitored and such movement sensed. The system further includes a head of train transceiver device linked to such brake equipment and connected to such brake pipe on such locomotive.

Abstract: A bleed valve for bleeding fluid from a hydraulic circuit comprises a valve body having a valve passage therethrough adapted for fluid communication with the hydraulic circuit, a valve seat on the valve body, and a sealing assembly. The sealing assembly has a valve closure connected to a valve stem and adapted for sealing engagement with the valve seat. The sealing assembly is moveable between a closed sealing position in which the valve closure sealingly engages the valve seat to block fluid flow through the valve passage and an open position in which the valve closure is spaced from the valve seat to permit fluid flow through the valve passage. A valve fitting on the valve body has an outlet port for exhausting fluid from the valve passage. The fitting is moveable relative to the valve body for selectively positioning the outlet port with respect to the valve body. The outlet port is in fluid communication with the valve passage regardless of its relative position with respect to the valve body.

Abstract: An automated terminal test system and performs a terminal test of brake equipment on a train. The system includes a test control box connected to a head of train locomotive and accessible from outside of such locomotive. Linked to such brake equipment, the test control box has a control for activating the test control box, applying and releasing the brakes, and charging and venting such brake pipe. The system also includes an end of train transceiver device connected to such brake pipe on a last railcar of such train. The end of train transceiver device monitors pressure within such brake pipe on such last railcar, senses movement of such last railcar, and communicates signals representative of such pressure monitored and such movement sensed. The system further includes a head of train transceiver device linked to such brake equipment and connected to such brake pipe on such locomotive.

Abstract: An automated terminal test system for performing a terminal test of brake equipment on a train includes a test control box connected to a head of train locomotive and accessible from outside of such locomotive. Linked to such brake equipment, the test control box has a control for activating the test control box, applying and releasing the brakes, and charging and venting such brake pipe. The system also includes an end of train transceiver device connected to such brake pipe on a last railcar of such train. The end of train transceiver device monitors pressure within such brake pipe on such last railcar, senses movement of such last railcar, and communicates signals representative of such pressure monitored and such movement sensed. The system further includes a head of train transceiver device linked to such brake equipment and connected to such brake pipe on such locomotive.

Abstract: An electro-pneumatic brake control system for a railroad freight car comprises application and release solenoid valves controlled by a microprocessor overlayed with the conventional car automatic pneumatic brake control system, including control for bleeding off auxiliary reservoir pressure at least during a power failure mode of operation during which the pneumatic brakes become effective to apply the car brakes in response to an induced brake pipe pressure reduction in the course of indirectly supplying brake pressure on cars having operable electro-pneumatic brakes. The bleed of auxiliary reservoir air pressure allows a subsequent slow recharge of the brake pipe pressure to create a positive release pressure differential across the control valve service piston to assure a brake release of the automatic pneumatic brake application to obviate a "stuck brake" condition on a car experiencing an electro-pneumatic power failure.

Abstract: A pneumatic receptacle adapted to receive a pneumatic connector head of a test device is mounted in a universal location remote from the brake control valve of a railroad freight car. The remotely mounted receptacle may be located on the railroad car body, for example, and is communicated with access ports associated with the control valve via hoses or conduits. In locating the receptacle on the car body, hook-up of the test device can be accomplished conveniently and in a safe manner by railroad personnel in the course of conducting a single car test to check the condition of the car brakes, regardless of the control valve location.

Abstract: A brake pipe pneumatic valve attachable to an end of a railway vehicle having a first flexible air hose for transmitting brake pipe pressure, and the end-of-train device with a second flexible air hose. The valve includes a housing having first, second, and third ports. The first port is releasably connectable to the first flexible air hose; the second port is releasably connectable with the second flexible air hose; and the third port is releasably matable with a coupling connected to a helper locomotive brake pipe. The valve includes a piston that divides the housing into first and second chambers. The first chamber communicates with the first and third ports; the second chamber communicates with the second port. Also, the piston has a channel therethrough connecting the first and second chambers. The valve further includes first biasing means, disposed between the housing and the piston, for selectably urging the piston towards sealing the first port.

Abstract: In a power-brake system, a hydraulic pressure generated by means of a pump may be supplied, controllably in proportion to an actuation force via brake conduits, by a power-brake valve to individual brake cylinders. Control pressure conduits are connected to the brake cylinders or the brake conduits in the vicinity of the brake cylinders and these control pressure conduits are connected to the brake valve. The brake pressure at the brake cylinders may be fed back, via the control pressure conduits, as the control pressure for acting on the control end of the brake valve so that a control of the control plungers of the brake valve is carried out corresponding to the brake pressure build-up at the brake cylinders and, particularly when low brake pressures are desired, rapid pressure build-up times in the brake conduits are ensured.

Abstract: A brake pipe pressure control system for a railroad train including a regulating valve device under control of a microprocessor wherein the regulating valve device is housed in the existing end-of-train device and effects service and emergency reductions of brake pipe pressure from the rear end of the train in correspondence with service and emergency reductions initiated at the locomotive.

Abstract: A braking system including a brakepipe control valve which controls pressure on a brakepipe in response to braking pressure signal from an electropneumatic converter. An electropneumatic cutoff valve connects the control valve to the brake pipe. A controller controls the converter and cutoff valve. A parking brake system and retarder control system are also included and are controlled by the controller.

Abstract: Apparatus for indicating the condition of hand brakes on railway cars and for applying and releasing railway car parking or hand brakes automatically in response to predetermined conditions including movement of a train, wayside conditioning apparatus, wayside operating mechanism, a signal controlled by an operator and performance of predetermined railway operating procedures, such as completion of an air brake test procedure. The apparatus may respond to mechanical, electrical and electronic signals and may operate on pneumatic or electric power provided from the service air brake system of a train or from a source of power outside of such air brake system.

Abstract: A remote handle operating mechanism for a cut-out cock located on the back side of a pipe bracket on which the service and emergency portions of a railroad brake control valve device are mounted at the front side thereof. A push-pull rod extends from the cut-out cock actuating lever via an opening in a detent bracket to the front of the pipe bracket to facilitate operation of the cut-out cock. A locking rod affixed to the push-pull rod co-acts with the detent bracket to latch the push-pull rod in either one of two positions corresponding to the open and closed positions of the cut-out cock to prevent inadvertent operation of the cut-out cock.

Abstract: An end of train railroad air hose having audible warning device which is powered by air from the air brake line and is actuated by the operator from the end of the train. The audible warning device may be located remotely from the operator via an elongated flexible conduit.

Abstract: A braking system is improved by addition of a spring brake pressure protection valve, to prohibit pressurization of the spring brakes prior to the build up of sufficient pressure to insure complete release of the spring brakes. This prevents the significant problems associated with known systems that permit operation of a tractor trailer with partially released spring brakes, which will cause unnecessary wear and reduced fuel economy. The spring brake pressure protection valve is located between the reservoir and the spring brakes, most preferably between the spring brake quick release valve and the spring brakes, or alternately, between the reservoir and the spring brake quick release valve.

Abstract: A hydraulic brake system that has a hydraulic unit for evacuation prior to initial filling, with the primary and secondary circuits dry, the brake system is equipped with special check valves, which are disposed between the primary circuit and the secondary circuit. When the brake system is evacuated, these check valves are in the open position, so that air escapes from the secondary circuits. This makes it unnecessary to open electromagnet valves, which are closed when without current and are present in the brake circuits I and II, electrically. The hydraulic brake system is intended for use in motor vehicles, and its hydraulic unit is designed to carry out anti-lock operation and/or traction controls.

Abstract: An access plate mounted between the pipe bracket portion and either the service portion or the emergency portion of a railway freight brake control valve. Passageways are provided through the access plate, each passageway terminating in a respective access port along an end of the access plate. Openings extend through opposed sides of the access plate, intersecting respective access plate passageways. The openings on each side are sized and positioned to sealingly align with openings of the pipe bracket portion and either the emergency portion or the service portion. The openings on the pipe bracket portion, emergency portion and service portion connect to passageways communicating to the brake pipe, the brake cylinder retaining valve, the brake cylinder, the emergency reservoir and the auxiliary reservoir. A housing may be attached to the pipe bracket portion to connect to the access ports, such housing preferably having a valve means for preventing the escape of fluid pressure therefrom.

Abstract: An electro-pneumatic brake system for a railroad freight car is integrated with the existing pneumatic freight brake system by utilizing the air stored in the emergency reservoir to supply brake cylinder pressure via the exhaust passage of the pneumatic control valve, which is maintained in release position during electro-pneumatic brake operation. The electro-pneumatic brake system fails to a release mode, so that the brakes on an individual car that experiences a power loss do not apply. In the case of a power loss in the electro-pneumatic system, due to a train break-in-two, the pneumatic brake system is automatically operated by the consequent loss of brake pipe pressure to provide a back-up brake, while at the same time interrupting the control valve exhaust path via which the electro-pneumatic brake is communicated with the brake cylinder.

Abstract: A brake control mechanism allows the engineman in a lead locomotive to control the brakes of a helper locomotive and does not require a manual connection of the brake pipe of the train to that of the helper locomotive. The End of Train (EOT) unit is used to effect this control. The EOT transmits brake pipe pressure data sensed at the end of the train. Both the lead locomotive and the helper locomotive are equipped with Head of Train (HOT) units which receive the transmitted data from the EOT unit. In the case of the HOT unit in the lead locomotive, this data is processed and displayed for the engineman in that locomotive, as is the normal operation in those units. However, in the case of the HOT unit in the helper locomotive, that unit is first of all set to receive the transmitted data from the EOT unit by dialing in the identification (ID) of the EOT unit using thumbwheels on the HOT unit provided for that purpose.

Abstract: A railway car vent valve device having a nullifier valve that is selectively operable to disable the vent valve device during a single car test procedure in which the service stability of the car control valve is checked. The nullifier valve is automatically reset when the car brake pipe pressure drops below a predetermined value, such as occurs when the single car test apparatus is disconnected from the car brake pipe following completion of the single car test procedure.

Abstract: A quick service limiting valve device for a freight brake control valve employing a primary valve in a fluid flow path via which brake pipe air is connected to the brake cylinder during a secondary phase of quick service to propagate the brake pipe reduction signal until the brake cylinder pressure acting on the limiting valve control piston effects closure of the primary valve to terminate the quick service flow of brake pipe air to the brake cylinder when a predetermined brake cylinder limit pressure is realized. A secondary valve is arranged to interrupt the brake pipe to brake cylinder flow path downstream of the primary valve in the event leakage at the primary valve causes the pressure acting on the quick service limiting valve control piston to exceed the predetermined limit pressure.

Abstract: This invention improves the capability of bleeding a chamber, disposed in the course of a line, that receives pressure fluid. On the pressure side of a high-pressure pump that pumps pressure fluid through a line, a chamber of circular-cylindrical cross section is disposed in its course. Two line segments of the line discharge into the upper face end of the chamber. A guide body disposed coaxially with the longitudinal axis of the chamber is received in the chamber in the region of this face end. The guide body embodied substantially in the form of a circular disk, defines an annular gap toward the inside circumference of the chamber and a subchamber of the chamber toward the face end of the chamber. The guide body directs air located in the chamber into the subchamber, from which it is carried away by the flow of pressure fluid. The hydraulic brake system is especially suitable for motor vehicles.

Abstract: The invention relates to a bleed valve for a hydraulic circuit, comprising a piston capable of sliding in a bore formed in a body and actuating a shutter arranged between two sub-circuits and movable between a first position, in which it allows communication between the two sub-circuits, and a second position, in which it prevents this communication, the shutter being movable under the effect of an external mechanical action exerted by an actuating member. According to the invention, the sealing between the bore and the outside of the body is ensured by the actuating member, and the shutter is movable under the effect of a difference between the pressures which are exerted on its two faces.

Abstract: An improved railroad train braking system causes automatic braking of cars which have been isolated from the braking control of the engineer. A safety apparatus (18), having structure permitting discharge of pressurized air from the system at a predetermined rate, is coupled at the rearmost end of a train brake pipe (26). Pressurized air from the braking system of cars located rearwardly of a closed aircock is permitted to discharge from the system through the safety apparatus. Air distribution control valves (40) in the affected cars (14, 16) sense the reduction in pressure, and active the brakes (42).

Abstract: A railway car vent valve device having a bleed valve that is selectively operable to disable the vent valve device during a single car test procedure in which the service stability of the car control valve is checked. The bleed valve is automatically reset when the car brake pipe pressure drops below a predetermined value, such as occurs when the single car test apparatus is disconnected from the car brake pipe following completion of the single car test procedure.

Abstract: A pressure relief valve for a railway emergency brake system that is simple in construction, easy to manufacture and to assemble and that, in operation, is self-cleaning of brake pipe dirt and debris. The inventive valve comprises a valve body having a hollow space being divided by a diaphragm into a first and a second chamber. Chambers are coupled via an orifice in the diaphragm, coupling pressure from the first chamber to the second. The valve comprises a peg aligned with the orifice, penetrating and cleaning the latter when the diaphragm moves from a closed position into an open position.

Abstract: A brake pipe continuity valve system permits the coupling of a pusher locomotive such that the engineer on the lead locomotive retains control of the entire train brake system including the pusher locomotive. The end-of-train device remains coupled to the air brake pipe line of the train, and a valve connects the air brake line pressure of the train with the air brake pipe of the pusher locomotive, upon moving the valve to an open position. The valve is automatically closed at the end of the pushing operation by the engineer on the pusher locomotive such that the brake pipe air remains intact throughout the main train including the end-of-train device, while isolating the pusher locomotive permitting it to back off at the end of the pushing operation.