GB2138906A - Pipe coupling - Google Patents

Abstract

In pipe couplings between sections of a long pipe comprising a multiplicity of sections connected in series by intermediate couplings, for example as found in the pneumatic brake pipe of a railway train, the sections are joined by flexible hoses terminating in coupling heads which are interengaged to provide a contiguous fluid passage. In order that the heads may uncouple themselves if the train is broken they include interlocking flanges 21, 22 which the fluid passages enter and exit through a right angled bend. The ratio of the bend radius to pipe bore is selected to lie within a range 1.5 to 6.0 and may be approximately 3.2 for optimum performance. <IMAGE>

Description

SPECIFICATION Pipe coupling This invention relates to a pipe coupling parti cularly for coupling together the brake pipes of adjacent vehicles in a train of vehicles fitted with a pneumatically controlled braking sys tem.

In a pneumatically controlled braking sys tem, of the type referred to, the operation of individual brake actuators is determined by fluid pressure in a common brake pipe. Dur ing a brake cycle there is movement of fluid in the brake pipe so that for efficient and rapid operation, particularly in respect of rapid propagation of fluid pressure variations along the brake pipe, it is desirable that the pipe possesses the lowest possible inherent resis tance to flow.

All couplings will tend to introduce some restriction to flow in the coupling as compared with the free flow through the pipes which are joined by the coupling.

Known couplings also involve many changes in cross-sectional area and the resultant expansion and compression of the flowing fluid cause substantial pressures losses.

This problem of restriction of flow arises because in most pipe couplings the internal diameter of parts of the coupling can be less than the diameter of the pipe in some places and greater in others, and may be accentuated by the fact that many pipe couplings, particularly those used for coupling pneumatic brake hoses used on railway trains and heavy vehicles, . incorporate sharp bends, in many cases 90' bends.

In the case of long railway trains this is of serious consideration because the length of the train is limited by the resistance which a brake pipe offers to fluid flow. Resistance is inversely proportional to diameter and a compromise standard diameter is chosen taking into account weight and other considerations, typically at one and a quarter inches. A main source of resistance lies in the couplings presently in use which present the major flow resistance in the pipe run.

Existing pipe couplings have a right-angled bend in each half of the pipe coupling. Obviously these right-angled bends introduce a great deal of resistance to flow.

According to this invention there is provided a pipe coupling comprising a pair of interlocking coupling heads which hold respective pipe terminations in sealing relationship by mutual engagement of interlocking flanged formations, one on each of the heads, and a curved pipe communicating with the termination of each coupling head having a ratio of bend radius to pipe bore equal to or greater than 1.5.

Preferably the curved pipe communication with the termination in a coupling head has a ratio of bend radius to pipe bore ratio substantially in the range 1.5 to 6.0. The reduced resistance of this coupling is very important because it will reduce the total resistance of the brake pipe and enable additional trucks or rail cars to be attached to a long train.In the accompanying drawings: Fig. 1 shows, in side view, a pair of brake hoses, between railway vehicles joined by an existing coupling; Fig. 2 shows a plan view of the coupling of Fig 1 with some parts in section; Fig. 3 shows, in side view, a pair of brake hoses joined by a coupling in accordance with the present invention; Fig. 4 is a sectional elevation through the centre of the coupling of Fig. 3; Fig. 5 is a section through one coupling head or one half of the coupling of Fig 3; Fig. 6 is a plan view, partly in section, of the pipe coupling of Fig 3; Fig. 7 is an enlarged elevation of a hose nipple used with the coupling of the present invention; and Fig. 8 is a graph indicating the relationship between resistance to flow and the ratio of bend radius to pipe bore.

In Fig. 1 and 2 is shown a standard train pipe or pneumatic brake pipe coupling which comprises two twenty two inch long hoses 10, 11 each of one and a quarter inch diameter joined by a coupling generally indicated at 12 which is in two easily separable parts. The two separable parts of the coupling are the coupling heads indicated at 13, 14 in Fig 2. Air flowing into the coupling head 13, from one of the hoses 11, flows along passage 15 and then turns through a right angle before passing through the coupling head orifice at 16. The air then enters coupling head 14, which is similar in internal shape to head 13, and again the air has to turn through a right angle to exit at 17 into the other hose 10.

These right angled bends introduce considerable restriction and losses in the coupling.

Fig. 3 shows two similar hoses IOA, 1 OB, joined by a pipe coupling 1 2A constructed in accordance with the invention. The included angle between the hoses, as shown, is substantially a right angle, i.e. the curved pipe of each coupling head is set at approximately 45 to a common horizontal plane.

The coupling heads are shown in more detailed in Figs 4 and 6. Each coupling head is formed with a shaped flange formation comprising an undercut lip 21 and a lug 22 on opposite sides of the coupling orifice 16.

When the coupling heads are interlocked the lug 22 on each head is manoeuvred into engagement under the lip 21 of the other head by mutual rotation of the heads while the two curved pipes are held in register to form a single continuous passageway. An endstop 23 is formed at one end of the lip 21 to limit the relative rotation of the heads. In Fig 4 the lug 22B may be disengaged from under lip 21A, and simultaneously lug 22A form under lip 21 B by clockwise rotation of pipe I 4B and anti-clockwise rotation of pipe 14A.

The hose IOA terminates at 19 in an easy bend 1 4A which has a radius of one and a half times the pipe diameter, so that, for a one and a quarter inch diameter pipe, the bend radius is three inches: A steel one and a quarter inch bend/hose nipple 20 as shown in Fig. 6, is normally fitted to the distal end of the curved pipe 1 4A, 1 4B for the attachment of the coupling hoses 1 OA and 1 or.

As may be seen in Fig. 7 the air flow through coupling parts 18 is direct without the abrupt 90 bends present in the type of coupling illustrated in Fig 2, and without changes of diameter which would introduce resistance to flow.

Besides offering greatly reduced resistance to air flow, because the abrupt 90 bends of the known coupling are eliminated, the angle at which the curved pipes 1 4A, 1 4B are inclined to the common horizontal plane means that the coupling can be undone by lifting it until the said pipes rotate into a substantially horizontal plane. Thus, the coupling will uncouple gently in the event of a break-away or when one wagon is decoupled from another, say in a marshalling yard, when the coupling is lifted under the influence of tension in the connecting hoses attached to the separating vehicles.

As previously mentioned the ratio of bend radius to pipe bore has great influence upon the resistance to fluid flow through a coupling, Fig 8 illustrates the effect of this on the total resistance of a curved pipe having a total bend of 90'. The total resistance is produced by the aggregate of the contributions of several factors: the turbulence inherent in the enforced change of direction of fluid flow is one factor and the viscous drag of fluid flow in a pipe is another. In the diagram the effect of the second of these factors is indicated by the line referenced "length resistance" and the effect of the first by the line "bend resistance".

The graphs represent a fluid flow passage having a right angled bend and constant internal bore diameter, however, the greater is the radius of the bend the greater is the length of the passage travelled by the fluid flow in the course of the bend. In the case of bends having short radii the bend resistence is overwhelmingly significant, whereas in the case of very long and easy bends, with long radii, the greater proportion of resistance is introduced by the length of the passage, whilst the resistance due to the bend itself decreases progessively. The curve of the total resistance, it has been found, therefore exhibits a minimum at a bend radius to pipe bore ratio value of approximately 3.2, although the total resistance within a range of values of 1.5 to 6.0 are also found to be acceptable.The graph shows that a coupling of this type having a value in the range 1.5 to 6.0 is equivalent to the inclusion of an additional length of 12 to 15 pipe diameters in a straigh train pipe.

Although described as applied to railway use the hose coupling may be used in other areas wherever air or other fluid under pressure has to be conveyed through a readily uncouplable coupling e.g. in road vehicles employing trailers, in pneumatic air lines supplying air to tools such as pneumatic drills, pipe lines and hose pipes on fire engines etc.

In railway use the particular points to be noted are that the coupling provides: (i). An easy bend of mean radius greater than one and a half pipe diameters which may be attached to any standard coupling mechanism. The coupling flanges used may be designed and manufactured in accordance with those laid down as standards so that it is possible to mix existing couplings, to the same standard design, with those embodying the invention.

(ii). The hose outlet is preferably offset 30 to the horizontal axis of the closed coupling.

That is each pipe lies in a plane inclined at 30 to a common, horizontal, plane through the coupling and, as previously described.

This can facilitate uncoupling greatly particularly, which is required to occur upon breakaway of railway vehicles and motor vehicle trailers.

(iii). The hose outlet is offset by at least one and a half pipe diameters from the mating faces but it may be brought back close to the mating plane by a further easy bend, so that pipes to be joined are mutually aligned.

Claims (6)

1. A pipe coupling comprising a pair of interlocking coupling heads which hold respective pipe terminations in sealing relationship by mutual engagement of interlocking flanged formations, one on each of the heads, and a curved pipe communicating with the termination of each coupling head having a ratio of bend radius to pipe bore equal to or greater than 1.5.

2. A pipe coupling as claimed in Claim 1 wherein the curved pipe communicating with the termination in a coupling head has a ratio of bend radius to pipe bore substantially in the range 1.5 to 6.0.

3. A pipe coupling as claimed in Claim 1 or Claim 2 wherein the coupling heads are interlocked the curved pipes lie in respective planes inclined to a common plane, but extending in substantially opposite directions, at angle in the approximate range of 30 to 45

4. A pipe coupling as claimed in any pre ceding claim wherein the curved pipe includes further curved portions the distal ends of which are substantially aligned and which have further bends having a bend radius to pipe bore substantially in the range 1.5 to 6.0.

5. A coupling head comprising one half of a pipe coupling in accordance with any preceding claim.

6. A pipe coupling or coupling head substantially as hereinbefore described with reference to the accompanying drawings.