MXPA98006032A - Dual seal coupling to allow the rapid measurement of the fren cylinder pressure - Google Patents

Abstract

The present invention relates to a dual seal coupling apparatus to allow rapid measurement of pressure through a receiver assembly of a car control valve, such assembly has a cover, a receiving body and at least one valve of verification installed in such receiving body where the check valve is reached upon removal of the cover, the check valve is normally compressed against a check valve seat formed in the receiving body to provide a first seal to prevent leakage of the pressure and that when removed from the seat of the check valve provides access to such pressure, the apparatus is characterized in that it comprises: (a) a cover of the receiver assembly that defines in itself a threaded bore generally aligned axially with the check valve when the cover is secured to the receiving body, and (b) a portion of the fast coupling coupling, such a male portion including (i) a valve body which itself defines a valve bore and having a threaded end for engaging in such a threaded bore and an opposite end for coupling with the female portion of the coupling of quick connection and (ii) a valve stem within the bores with a head end therein that is normally compressed against a valve stem seat formed in the valve body to provide a second seal which also prevents the leakage of such pressure, but when the female portion engages with the male portion, the valve stem moves from the seat of the check valve and provides access to allow measurement of such pressure.

Description

DUAL SEAL COUPLING TO ALLOW THE RAPID MEASUREMENT OF THE PRESSURE OF THE BRAKING CYLINDER.

CROSS REFERENCE FOR RELATED APPLICATIONS.

This request is related to the North American co-pending application entitled Dual Seal Fitting for Enabling Quik Measurement of Braket Cylinder Presure, with Serial Number 08 / 901,096, currently deposited with it on July 28, 1997. The co-pending application is assigned to the transferee of the present invention, and its teachings are incorporated for reference herein.

FIELD OF THE INVENTION The present invention is generally related to a mechanism through which access to a pressure to be measured is obtained. More particularly, the invention relates to an apparatus that allows the rapid measurement of the pressure of the braking cylinder through a receiver assembly of a pneumatic control valve of a wagon.

BACKGROUND OF THE INVENTION A typical freight train includes one or more locomotives, a plurality of wagons and a pneumatic train line known as a braking tube. The braking tube consists of a series of long individual tubes interconnected with each other. A tube that is secured to the bottom of each car is interconnected to another tube by means of a coupler located between each car. The braking tube supplies the pressurized air needed by the braking control system to charge several reserves or tanks and operate the air braking equipment in each wagon of the freight train. The operator in the locomotive can manipulate the parking brake to apply and release the brakes on the wagons as desired. The parking brake can be applied in a released position at one end where the braking tube pressure is at maximum and the brakes are in an emergency position at the other end where the braking tube pressure is at a minimum and brakes are applied in full. In this way, the handbrake positions include the release of the brake, the minimum application of the braking service, the total application of the braking service and the application of the emergency brakes. When the brakes are released, the reserves and the braking tube are usually charged at the same pressure: usually at 90 psi in a freight train and at 110 psi in a passenger train. When the brakes are applied, the pressure in the braking tube is reduced by means of a valve located in the main locomotive. The exact amount at which the pressure is reduced depends on, in which application position the handbrake is located. It is this pressure reduction that indicates the brake control valve in each car to supply pressurized air from the appropriate reservoir (s) for the brake cylinders. The braking cylinders convert this pressure into mechanical force applied by the brake shoes to reduce or stop the rotation of the wheels of the car. Assuming that the brake signal is transmitted successfully throughout the train, the brakes of all the wagons in the train respond in the same way generally. The braking equipment in each wagon of a freight train typically includes one or more braking cylinders, an emergency reserve of air, an auxiliary air reserve and a conventional pneumatic braking control system such as the "ABD" or control valves. similar control. Each wagon can also include full and empty load braking equipment such as the Proportional Load Valve Pl and the Load Sensor Valve Sl, which are produced in the Estinghouse Air Brake Company (ABCO) and which are known in the art. of the braking control. The figure is illustrated by a schematic diagram of an ABD pneumatic brake control valve. Such a control valve includes a service portion and an emergency portion typically mounted on opposite sides of a tube fork. It should be noted that there is at least one other type of tube fork in which the service and emergency portions are mounted on the same side. Whether dealing with the dual-side or single-sided variety, the tube fork comprises a number of internal passages and several ports. Each port is connected to one of the tubes that are interconnected from the car, such as those that reach the braking tube, the braking cylinder, the emergency tank and the auxiliary tank. It is through these ports and the internal passages of the tube fork that the relevant portions of the control valve communicate fluidly with the pneumatic tube in the car. The service and emergency portions of the pneumatic control valve operate in accordance with the principles already known in the railway industry. The service portion of the control valve performs different functions, including: (1) controlling the flow of air from the auxiliary reservoir to the brake cylinder during a braking service application, (2) controlling the replenishment of auxiliary reserves of emergency, and (3) control the wear of the brake cylinder when the brakes are released. The emergency portion of the control valve controls, among other things, the air flow between both reservoirs up to the braking cylinder during the application of the emergency brakes. The North American Railway Association (A.A.R) issued the specification S-486-91, which details the basic test procedures that must be performed periodically on the braking equipment of each car. It is necessary that leak tests are made on the braking equipment. There is a standard A.A.R test device that can be used to perform such a test, however, it is very complicated and requires the interpretation of a very experienced user to identify braking equipment problems. Accordingly, in the North American Application Serial No. 08 / 365,815, WABCO described and claimed an automated car tester that can carry out the necessary tests more quickly and reliably than the standard A.A.R test device. Such copending application is assigned to the assignee of the present invention, and its teachings are incorporated by reference in this document.

Among other functions, the automated car tester is used to measure the pressure of several points within the brake control system of the car. The one-sided fork of the tube has a receiver assembly mounted on the same side of the fork of the tube in which the service and emergency portions of the control valve are mounted. Such a receiver assembly provides the automated car tester with quick and direct access to certain internal passages of the fork and subsequently, to the pneumatic tubes and reservoirs whose pressure must be tested. Specifically, through the receiver assembly, the automated car tester can measure the pressure inside the brake cylinder, the brake tube, the emergency tank and the auxiliary tank. However, the dual-sided tube fork has its ports located at the rear. Consequently, it is very difficult to access the ports and the pipes that connect them; therefore, for wagons equipped with the dual-sided tube fork, the automated car tester is used in conjunction with a combination access and receiver assembly. Such an access plate portion of the assembly is typically connected between the fork of the tube and the serving portion of the control valve as shown in Figures la and lb. The receiving portion is assembled as shown in Figure Id. Connected to form the combined assembly as shown in Figure lb, the receiving portion together with the access plate allows access to the internal passages of the tube fork. For wagons equipped with dual-sided tube forks, the combined assembly is the part through which the automated tester can measure the pressure inside the braking cylinder, the braking tube, the emergency tank and the auxiliary tank. . It will be apparent from the following description and claims that the receiving portion and the receiving assembly of the two aforementioned tube forks are identical except as regards the immaterial of the present invention. For this reason, the terms "receiver assembly" and "receiving portion" should be used interchangeably. As shown in Figure Id, the receiver assembly includes a cover, a receiver body and four verification valves installed in defined bores in the receiver body. Each check valve basically includes an insert made of rubber or other suitable seal material, a carrier that holds the insert and a spring. A packing is also used and usually a filter with each check valve. Consequently, each check valve is normally compressed against the check valve seat formed in the upper part of the hole. When the receiver assembly is mounted on the control valve, the check valves, at the head of the receiver body, become accessible by removing the cover. Each check valve serves as an access door through which the pressure contained in one of the following devices enters: braking cylinder, braking tube and the emergency and auxiliary reserves. Even with the cover already removed, each check valve acts as a seal, preventing the leakage of air under pressure. The Automatic Single Carrier Tester includes a pneumatic connector designed to couple with the upper part of the receiving body and through that to each of the four access ports. By moving each check valve away from its check valve seat, the tester can load and measure the pressure with the brake cylinder, the brake tube, the emergency tank and / or the auxiliary tank. The A.A.R proposed that each wagon of a freight train had a mechanism that allowed the pressure inside the braking cylinder to be read quickly. Currently, A.A.R. is considering issuing a specification that requires that the quick connect tools that are on the market be used to access the pressure inside the braking cylinder. However, the disadvantage of such tools is that they provide only a seal in which the pressure to be measured is contained. That is to say, that while a tool is not being used to access the pressure, such a tool offers only a seal to prevent the leakage of the pressure that it supposedly contains. Unless the tools are routinely covered to protect the seal when the tools are not being used to access the brake cylinder pressure, the seal is exposed to dust, dirt and / or other potential contaminants. Of course, it is important that such tools prevent pressure leakage from the brake cylinder, otherwise the operation of the brakes could be seriously affected. It should be noted that the following background information is provided to assist the reader in understanding this invention. Accordingly, any term used therein is not intended to be limited to any particular narrow interpretation, unless specifically stated otherwise in this document.

OBJECTIVES OF THE INVENTION Therefore, the primary objective of the invention is to provide an apparatus that allows the pressure inside a braking cylinder of a car to be measured quickly. Another objective is to pour the pressure into the brake cylinder quickly, measurable with an apparatus comprising two seals, so if one seal must be removed, the other will prevent the leakage of air that the device is supposed to contain. Another object is to provide such an apparatus with a male portion of a quick connect fitting that is commercially available, so that the pressure within the braking cylinder can be quickly measured by coupling the male portion with its corresponding female portion and in which a pressure measuring device was attached to its other end. Another object of the invention is to provide a dual seal coupling apparatus to allow rapid pressure measurement within one of the braking cylinders, the braking tube, the emergency tank and the auxiliary tank in the wagon. In addition to the objects and advantages listed above, several other objects and advantages of the invention will be more apparent to those skilled in the relevant art of reading the detailed description section of this document. The other objects and advantages will be particularly apparent when the detailed description is considered together with the accompanying drawings and the appended claims.

SUMMARY OF THE INVENTION In a current preferred embodiment, of the present invention provide a dual seal coupling apparatus to enable rapid measurement of the pressure of the brake cylinder through the receiver assembly of a pneumatic control valve of a car. The receiver assembly has a cover, a receiving body and at least one verification valve installed in the receiving body. The check valve can be accessed when removing the cover. Normally the check valve is compressed against the seat of the check valve, formed in the receiving body to provide a first seal that prevents the leakage of the pressure. When removed from the check valve seat, it allows access to the brake cylinder pressure. The double seal coupling apparatus includes a protrusion protruding from the receiver body cover and a male portion of a quick connect coupling. The protrusion defines itself a threaded bore which generally aligns axially with the check valve when the cover is secured to the receiving body. The male portion of the quick connect coupling includes a valve body and a valve stem. The valve body itself defines a valve bore and has a threaded end to be screwed into the threaded bore of the cover. At its opposite end, the valve body is formed to mate with the female portion of the quick connect coupling. The valve stem moves within the bores and has one end of the head that is normally compressed against the valve stem seat formed in the valve body. The end of the head of the valve stem against the valve stem seat provides a second seal that also prevents leakage of brake cylinder pressure. When the female portion engages with the male portion, the valve stem is removed from the valve stem seat by moving the check valve seat check valve and allowing access for pressure measurement of the cylinder. braking.

BRIEF DESCRIPTION OF THE DRAWINGS Figure la is a schematic diagram of a pneumatic brake control valve of type ABD comprising an access and a receiver assembly. Figure lb is an exploded view of the pneumatic brake control valve of the ABD type illustrated in Figure la. The Figure is an enlarged perspective view of the receiver assembly illustrated in Figures la and lb. Figure Id is an exploded view of the receiver assembly illustrated in Figure le. Figure 2 is a cross-sectional view of a receiver assembly incorporating the dual seal coupling apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION.

Before describing the invention in detail, the reader is warned, for clarity and understanding, the identical components that have identical functions in each of the attached drawings were marked as far as possible with the same reference numbers in each of the Figures provided in this document. Each of the Figures la-d illustrates a receiver assembly 200 of a pneumatic control valve 300 of a car. The control valve 300 includes a service portion 400 and an emergency portion 500 mounted on a tube fork 301. Although Figures la and lb show the receiving portion 200 of the access and receiver assembly 190 used in connection with the fork of the vehicle. Dual side tube 301, it is again noted that in this document the term "receiver assembly" also encompasses the receiver assembly used in connection with the aforementioned single-sided tube forks (not shown). The receiver assembly 200 includes a cover 203, a receiving body 205 and four verification valves 210a-d installed in defined bores in the receiving body 205. As best shown in Figure Id, each check valve basically includes a formed insert 13a-d made of rubber or other suitable sealing material, a carrier 14a-d holding the formed insert and a spring 15a-d. Packs 7-10 and filters 16a-d are also used with check valves. Consequently, each check valve is normally compressed against the seat of a check valve, formed at or near the tip of its bore. When the receiver assembly 200 is mounted on the control valve 300 as indicated in Figures lb and Id, for example, the check valves, on the head 202 of the receiver body 205, are accessible by removing the cover 203. The valve of verification 210a serves as an access port through which the pressure enters the auxiliary and emergency reserves respectively. Each check valve acts as a seal preventing the leakage of the air pressure that is intended to be contained even when the cover 203 is removed. The valves 7 and 8 serve as a complement to the seal provided for each of the check valves 210a-d. Figure 2 illustrates the essential details of a current preferred embodiment of a dual seal coupling apparatus 100. The dual seal coupling apparatus 100 allows rapid measurement of brake cylinder pressure through a modified receiver assembly 600 of the pneumatic control valve 300 of the car. The receiver assembly 600 of the present invention is generally identical to the receiver assembly 200 shown in Figures la-d, except for the cover 603 illustrated in Figure 2 and described below.

The dual seal coupling apparatus 100 includes a modified receiver assembly 600 and a male portion 610 of a quick connect coupling. The modified receiver assembly 600 includes the receiver body 205 and the four check valves 210a-d disposed generally in the same manner as in the prior art receiver assembly 200. However, the cover 603 of the modified receiver assembly 600 that features a protrusion 613 protruding from the cover. The protrusion 613 defines in itself a cylindrical bore 614 whose wall is at least partially threaded to receive a threaded end 618 of the male portion 610 of the quick connect coupling. The threaded bore 614 is generally axially aligned with the check valve 210a when the cover 603 is secured with bolts or other means for receiving the body 205. The male portion 610 of the quick connect coupling that characterizes the body of a valve, a piece of rod of a valve and an extension. The valve body 616 defines in itself a valve bore 617 and includes the threaded end 618 which is inserted into the threaded bore 614 of the cover 603. The valve body 616 at its opposite end 619 is formed to engage a corresponding female portion (not shown) of the quick connect coupling. It should be noted that there is a variety of quick connect couplings commercially available in the market. Especially with respect to the threaded end 618, the size and dimensions of the particular quick connect coupling to be used with the present invention should be selected according to the size and dimensions of the cover 603 and its protrusion 613. The valve stem 620 part of the male portion 610 preferably has as a head end 621 a spring-type valve that is movable within the bore 617 of the valve. The spring valve of the valve stem part is normally compressed by a spring 622 against the stem seat 625 of the valve formed in the head end of the valve body 616. The extension 623 is located between the opposite end of the rod piece 620 of the valve and the tip of the check valve 210a of the brake cylinder pressure. Accordingly, when the female portion of the quick connect coupling engages with the male portion 610, the spring valve 621 is removed from the stem seat of the valve 625. In this manner, the rod piece 620 of the valve pushes against the extension 623. Subsequently extension 623 presses against check valve 210a, thereby removing the check valve from its seat 209a of the check valve. The coupling of the male and female portions of the quick-connect coupling thus provides an access for the pressure in the braking cylinder. The foregoing allows rapid measurement of the pressure by means of a pressure measuring device attached to the opposite end of the female portion of the quick connect coupling. The extension 623 preferably has grooves along the length to fold in cross section in a plane normal to the longitudinal axis of the extension in Figure 2. The grooves must allow the air to flow more smoothly through the male portion 610, which does not it would be the case with the absence of such slots. It seems that the male and female portions of the quick connect coupling can be interchanged. Specifically, the female portion, rather than the male portion, of the coupling must be designed to be engaged or otherwise secured in the protrusion 613 of the cover 603. The male portion, rather than the female portion, of the quick connect coupling would then be attached at its opposite end to the pressure measuring device. It also appears that the dual seal coupling apparatus 100 described herein can be applied not only to the check valve 210a of the brake cylinder but to one or more of the other check valves 210b-d. Only the cover 603 needs to be modified in almost the same manner as described above for the protrusion 613 to complete that objective. From Figure Id it can be seen that certain perforations of the check valves have diameters different from the diameter of the check valve 210a of the braking cylinder. Accordingly, the cover 603 will have to be designed to accommodate one or more protuberances of different diameters, the threaded ends of the male portion engaging in these protrusions must, of course, be dimensioned in the proper manner. Depending on how extensively the coverage 603 is modified, the dual seal coupling apparatus of this invention can be used to rapidly measure the pressure inside the brake cylinder, the brake tube, the emergency tank and / or the auxiliary tank. . In this way, the dual seal coupling apparatus 100 comprises both a primary seal and a backup seal to prevent leakage of brake cylinder pressure when the male portion 610 of the quick connect coupling is not engaged. Usually compressed against the seat 625 of the valve stem, the spring type valve 621 serves as the primary seal, since its position is that which is most exposed to dust, dirt and / or other potential contaminants. . Similarly, the check valve 210a is usually compressed against the seat of the check valve 209a. In this way, the check valve 210a provides a seal that serves as a backup in the event that the primary seal succumbs to such contaminants or degrades otherwise. On the other hand, if the seal of the check valve is degraded, the spring valve seal acts as a backup seal. The dual seal coupling apparatus 100 allows the pressure within the brake cylinder to be measured quickly. Although the invention makes the pressure of the brake cylinder accessible for rapid measurement, it maintains the complete integrity of the air brake equipment in the car by means of the primary and secondary seals that prevent air leakage from the brake cylinder. . The current preferred embodiment for carrying out the invention was set forth in detail in accordance with the Patent Act. Those persons who are knowledgeable in the art to which this invention pertains may, however, recognize several alternative ways of practicing the invention without departing from the spirit and scope of the appended claims. Those with such knowledge will also recognize that the following description is illustrative only and does not intend to limit any of the following claims to any particular narrow interpretation. Accordingly, to promote the progress of science and useful techniques, we ensure for ourselves through the Patent Documents, the exclusive rights of all the subject matter covered by the following claims for the period prescribed by the Patent Act. .

Claims (14)

1. A dual seal coupling apparatus to allow rapid measurement of pressure through a receiver assembly of a wagon control valve, such receiver assembly has a cover, a receiving body and at least one verification valve installed in such a receiving body where the verification valve is reached when the cover is removed; the check valve is normally compressed against a check valve seat formed in the receiving body to provide a first seal which prevents the leakage of the pressure and which when removed from the check valve seat provides access to such a pressure; the apparatus is characterized in that it comprises: (a) a cover of the receiving assembly defining in itself a threaded bore generally aligned axially with the check valve when the cover is secured to the receiving body; and (b) a quick connect coupling male portion, such a male portion including (i) a valve body which in itself defines a valve bore and having a threaded end for engaging in such a threaded bore and an opposite end for coupling with the female portion of the quick connect coupling and (ii) a valve stem movable within the bores with a head end therein that is normally compressed against a valve stem seat formed in the valve body for provide a second seal that also prevents leakage of such pressure, but when the female portion engages with the male portion, the valve stem moves from the seat of the check valve and provides access to allow measurement of such pressure .

2. The dual seal coupling apparatus according to claim 1, characterized in that the stem of the valve has a curved cross section.

3. The dual seal coupling apparatus according to claim 1, characterized in that the valve stem includes: (a) a valve stem member having at the end of the head a spring valve that is loaded against the valve. valve stem seat; and (b) an extension located between an opposite end of the valve stem part and the check valve that when the female portion engages with the male portion, the spring valve moves from the valve stem seat and the part of the valve stem pushes against the extension by moving the verification valve check valve seat and providing access to the pressure and allowing rapid measurement of it through a device attached to an opposite end of the valve. the female portion.

4. The dual seal coupling apparatus according to claim 3, characterized in that the extension has a curved cross section.

5. The dual seal coupling apparatus according to claim 1, characterized in that the pressure is at least one pressure of the braking cylinder, the pressure of the braking tube, the pressure of the emergency tank and the pressure of the auxiliary tank.

6. The dual seal coupling apparatus according to claim 5, characterized in that the pressure is the pressure of the braking cylinder.

7. A dual-seal coupling apparatus for enabling rapid measurement of pressure through a receiver assembly of a wagon control valve, such receiver assembly has a cover, a receiving body and at least one verification valve installed in the receiving body where the check valve is reached when the cover is removed; such a check valve is normally compressed against a check valve seat formed in the receiving body to provide a first seal that prevents pressure leakage and that when removed from the check valve seat provides access to such a pressure; the apparatus is characterized in that it comprises: (a) the cover of the receiver assembly defining therein a threaded bore generally aligned axially with the check valve when the cover is secured to the receiving body; and (b) a male portion of a quick connect coupling, said male portion includes (i) a valve body defining therein a bore of the valve and having a threaded end to engage in the threaded hole and a opposite end to mate with the female portion of the quick connect coupling, (ii) a piece of the valve stem having at the end of the head a spring valve movable within the valve bore which is normally compressed against a valve stem seat formed in the valve body to provide a second seal that also prevents leakage of pressure, and (iii) an extension located between an opposite end of the valve stem part and the valve of verification, so that when the female portion engages with the male portion, the spring valve moves from the seat of the valve stem and the stem part of the The valve pushes against the extension by moving the verification valve of the check valve seat and providing access and allowing rapid measurement of the pressure by means of a pressure measuring device attached to an opposite end of the female portion.

8. The dual seal coupling apparatus according to claim 7, characterized in that the extension has a curved cross section.

9. The dual seal coupling apparatus according to claim 7, characterized in that the pressure is at least one pressure of a brake cylinder, the pressure of a brake pipe, the pressure of the emergency tank and the pressure of the auxiliary tank.

10. The dual seal coupling apparatus according to claim 9, characterized in that the pressure is the pressure of a braking cylinder.

11. A dual seal coupling apparatus to enable rapid measurement through a receiver assembly of a wagon control valve, such a receiver assembly has a cover, a receiving body and at least one verification valve installed in the receiving body in where the check valve is reached upon removal of the cover, such a check valve is normally compressed against the check valve seat formed in the receiving body to provide a first seal which prevents pressure leakage and which when removed from the check valve. check valve seat provides access to such pressure, the apparatus is characterized in that it comprises: (a) a protrusion protruding from the cover of the receiver assembly and defining therein a threaded bore generally aligned axially with the valve of verification when the cover is secured to the receiving body; and (b) a first portion of a quick-connect coupling, said first portion includes (i) -a valve body defining therein a bore of the valve and having a threaded end for engaging the threaded bore and an opposite end for coupling with a second portion of the quick connect coupling, (ii) a piece of the valve stem having at the end of the head, a spring valve movable within the valve bore which is normally found compressed against the stem seat of the valve formed in the valve body to provide a second seal which further prevents the leakage of such pressure, and (iii) an extension located between an opposite end of the valve stem part and the check valve that when the first and second portions are engaged, the spring valve moves from the stem of the valve stem and the valve stem part press against the extension by moving the check valve of the seat of such check valve and providing access and allowing rapid measurement of such pressure by means of a measuring device attached to an opposite end of the second portion.

12. The dual seal coupling apparatus according to claim 11, characterized in that the extension has a curved cross section.

13. The dual seal coupling apparatus according to claim 11, characterized in that the pressure is at least the pressure of a braking cylinder, the pressure of a braking tube, the pressure of an emergency reserve and the pressure of a reserve auxiliary

14. The dual seal coupling apparatus according to claim 13, characterized in that the pressure is the pressure of a braking cylinder. SUMMARY OF THE INVENTION A dual seal coupling device allows rapid measurement of brake cylinder pressure through a receiver assembly of a control valve. The receiver assembly has a receiver body, a check valve installed in the body and a cover that when removed makes the verification valve accessible. The check valve is normally compressed against the check valve seat to provide a first seal that prevents the leakage of pressure. When removed from your seat, the check valve allows the entry of pressure. The apparatus includes a protrusion protruding from the cover and a male portion of a quick connect coupling. The protrusion defines a threaded bore aligned with the check valve when the cover is secured to the receiving body. The male portion includes the body of a valve and the stem of a valve. The valve body defines a bore of the valve and has a threaded end to engage in the threaded bore of the cover. At its opposite extreme, the valve body is formed to mate with the female portion of the quick connect coupling. The valve stem moves within the boreholes and its head is normally compressed against the valve stem seat. The head of the valve stem against the valve stem seat provides a second seal that also prevents the leakage of pressure. When the male and female portions are coupled, the valve stem moves from its seat so the check valve moves from its seat allowing the entry and measurement of the braking cylinder pressure.