Technical Contributions THE PRESSURE RETAINING VALVE BY WILL W. WOOD One of the details of the air-brake descending grade it can not be done, on equipment of every freight car in Amer- account of the comparative slowness of ica, and of thousands of passenger cars, auxiliary-reservoir recharge. It is necesis the Pressure Retaining Valve, or "re- sary to understand that under the most tainer" as it is commonly called; yet it is favorable circumstances when the resurprising how few railroad men know charge steadily maintains a brake-pipe exactly what the retainer is intended to pressure of no less than 70 pounds-the do when cut in for action. On non- auxiliary reservoirs will charge no faster mountain roads the trainman knows that than about one pound per second; and if the handle is left "turned up" it will in the 20 or 30 seconds necessary for full "stick the brake" after the next applica- recharge before reapplication the train tion-and that is about all the trainman on the mountain road knows about it, for that matter; but the mountain men know how to make use of this particular feature. would have time to get beyond control. But, with a train of any ordinary length the auxiliary reservoirs will not recharge near as quickly as one pound per second; so, to enable the engineer to recharge the auxiliary reservoirs after an application without entirely releasing the brakes, the pressure-retaining valve is provided. The retaining valve is only intended for use when descending heavy and long grades. If the brake cylinders on the cars were absolutely free from leakage, the retaining valve would not be necessary. But there is leakage; and no matter if close inspection does not reveal it, yet there is a certain amount-sometimes on passenger cars it is beside the door, or rapid-leakage around the piston packing-leather in the brake cylinder that can not be heard. a On a freight car the retaining valve is located near the hand brake where it can be easily reached by the trainman; and on the end of the vestibule,-outside, usually, with the valve stem, or "cock key," extended inward to permit locating the handle within the vestibule, all styles of passenger-car retaining valve being furnished, if so ordered, with extended cock key for this purpose. A pipe leads from the exhaust port of the triple valve to the retaining valve, and when the handle is turned in downward position the pipe has a continuous, free outlet to the atmosphere just as though the retaining valve did not exist. When And when an application is begun there is then no further source of air supply to the brake cylinder than that contained in the auxiliary reservoir on the individual car; therefore, after brake-pipe reduction and the brakes have held the train under control for a certain length of time, in down-grade work, and then, due to brake-cylinder leakage, the speed begins to pick up, a further reduction must draw the brake-cylinder the handle is turned up to a horizontal supply from a depleted auxilary reservoir; each continuing reduction still further lessening the pressure in the auxiliary reservoir, until shortly there is not enough air left to control the train and it gets away. position (referring now to the plain, twoposition retaining valve of the original style), the releasing brake-cylinder pressure from the triple valve can only escape by unseating a weighted valve, which permits pressure in excess of 15 pounds to escape, and then, seating, it to hold the car at the present low speed while the auxiliary reservoir is becoming recharged. But, if after the first application has brought the speed down to a low degree retains that amount in the brake cylinder "why not release and get the auxiliary reservoirs recharged quickly before the train has again gotten to an undesirably high speed?" This can be done where Fig. 1 is a two-sided sectional view of the gradient decreases considerably-at a a plain retaining valve of the weighted point on the hill where the road is nearly style. The handle is turned down in the level for a short stretch; but on the usual free release position. The pipe from ex haust port of triple valve connects with pheric port c and now connects port D port D in the body of the valve, and when the triple valve is in the release position the exhausting brake-cylinder air with port d under the weighted valve, and if the exhausting air from the brake cylinder is at a higher pressure than 15 With the advent of heavier cars, and shown in Fig. 2. In it there is an "inside particularly the modern steel freight cars weight," 4 (see cut), that acts the same that vary so greatly as between light when handle is turned up horizontally, weight and loaded weight, it became as described in reference to the plain re necessary not only to provide for retain- taining valve, holding a pressure of 15 ing a higher brake-cylinder pressure on pounds. The "outside weight," 10, is empty cars, but also to obtain a still held from resting upon the inside weight higher retained pressure when the car is by the support of "lifting rod" 9, which loaded. So the Double Pressure Weight is held up by contact with the eccenType retaining valve was introduced- tric form of the cock handle 5, except when the handle is placed in the interme- phere is plainly traced. When the handle diate or diagonal position represented in is turned up to the horizontal position, the plate as "high pressure," at which the exhaust air pressure must raise and time the outer weight drops upon the inner weight, and together they give a resistance that requires an air pressure of 30 pounds to lift the valve. The same type of retaining valve is also made to give a resistance of 25 and 50 pounds, for use on cars of 100,000 pounds or greater, capacity. The spring type of retaining valve has succeeded the weight type as being more reliable in seating. Fig. 3 represents a single-pressure retaining valve of the "spring type," and as it operates the same as the weight type-a spring of the required resistance taking the place of the weight upon the valve-further explanation is unnecessary. pass the left-hand valve which is set at 25 pounds, reaching the atmosphere at the exhaust port in cap nut as shown. When the handle is turned half-way upto the high-pressure position, HP-the exhausting pressure must first unseat the right-hand valve, then flow to the lefthand valve and unseat it in order to escape to the atmosphere from the port shown in the cap nut of the left-hand valve (there being no exhaust port above the right-hand valve); and as the springs on both valves have a resistance of 25 pounds each, the total resistance to the brake-cylinder pressure escaping to the atmosphere will now be 50 pounds. In overhauling this retaining valve no error can occur from exchanging the springs, as they are both exactly alike. In Fig. 4 is represented a Double This type of retaining valve is made to retain pressures of 10-20, 15-30, or 25-50 This engine runs on the branch line between Jamestown, Cal., and Angels Camp. It climbs a 4 to 4% per cent grade and will go around any curve that a box car will. The Hotel Nevills at Jamestown is shown in the background. (Courtesy of Bro. Al Lagomarsino, Lodge 808) NEW YORK AIR BRAKE EQUIPMENT* BY JOHN HAMILTON Blows in the LT Locomotive Brake Equipment. control valve should be closed and the the control-valve reservoir gasket into the may leak permitting auxiliary-reservoir pressure to pass to the retain pipe, or it may be due to a leak of main-reservoir pressure or brake-pipe pressure through the control valve reservoir gasket, permitting the above pressures to reach the passage in the control valve leading to the control reservoir and then by the retain pipe to the automatic brake valve. Blows in the LT locomotive brake air brake valve. Brake-pipe leakage by equipment will next be considered. There are four points at which these may occur, namely, at the exhaust port of the control valve, at the direct exhaust, or brakepipe exhaust port of the automatic brake valve, and at the exhaust port of the straight-air brake valve. A blow at the exhauset port of the control valve may be caused by a leak from the main reservoir or the brake pipe. Brake-pipe leakage at the control valve exhaust port could occur past the slide valve in the quick-action cylinder cap into the passage which leads Should a blow occur at the direct-exto the brake cylinders, or past the gasket haust port of the automatic brake valve in the triple-valve cylinder cap into the with this valve in running position, it same passage, or through the control may be caused by a leak from the main valve gasket, the leakage in this case reservoir, brake pipe, or from the control. being from the brake pipe into the passage valve auxiliary reservoir. This may be leading to the brake cylinders. Leakage due to a leak of main-reservoir pressure of main reservoir pressure at the exhaust by the rotary valve in the brake valve, port of the control valve could occur the triple-slide valve in the control valve through the control valve gasket from the main reservoir into the passage leading to the brake cylinders, by the preliminary admission valve or by the admission valve in the control valve. It can be determined, whether this leak is from the main reservoir or the brake pipe by closing either the brake pipe or main reservoir cut-out cock, and if the blow soon stops when one of these cocks is closed the escaping air must have been coming is from the control valve or from the from the source that had been cut off. brake valve by closing the cut-out cock With the brakes applied, a leak of main in the brake pipe and in the main-reserreservoir pressure at the points above voir pipe to the control valve and then named would pass to the brake cylinders drain all pressure from the control valve. as the exhaust valve now has the exhaust If the blow stops the air is coming from port blanked. There will then be an inter- the control valve, whereas if it continues mittent blow at the exhaust port of the the leak at the direct exhaust port is due control valve as the brake-cylinder pres- to the rotary valve leaking. It can also be sure will be raised above the pressure in ascertained whether the blow at the direct the control reservoir, forcing the control exhaust port of the brake valve is caused piston towards release position, opening by a leak through the rotary valve or the exhaust port and permitting the brake- from the control valve due to leakage cylinder pressure to escape until it falls through the control valve gasket into the slightly below the pressure in the control control reservoir, or past the slide valve, reservoir, when the control piston will by uncoupling the retain pipe at the conagain move and cause the exhaust valve trol valve and noting the direction in to blank the exhaust port. Should the pre- which the escaping pressure is coming. If liminary admission valve or admission the blow is down through the brake valve valve stick open, the effect would be the it would indicate a leak through the same, as air at main-reservoir pressure rotary valve into port h. The defect will will have a direct passage to the brake be found in the control valve if leakage cylinders. In the above cases, the cut-out is occurring at the retain pipe connection cock in the main reservoir pipe to the to this valve.. * Continued from October, 1914, Magazine. It can be determined whether the blow Should a constant blow occur at the control valve exhaust port when the loco |