IE980821A1 - A tapered pipe connector - Google Patents

Abstract

A coupling having a bored parallel threaded female ferrule (1) for mounting on a threaded tapered fitting (10). The precise length of the female thread (5) has been determined by theoretical and practical analysis to ensure that a seal (7) interposed between ferrule (1) and fitting (10) is correctly compressed with the parts tightened together.

Description

The present invention relates to pipe couplings and in particular to pipe couplings for mounting on tapered threads.

There are considerable advantages, particularly sealing advantages in the use of male tapered threads on pipe ends and pipe fittings which are connected to other fittings, flanges, couplings and the like, often generally referred to as adapter ferrules, which have an internal parallel thread.

While these connectors are advantageous fitted to tapered threads they suffer from the problem that there is no precise control of the travel of the female ferrule onto the tapered threaded bored male fitting. Thus, there is often a spacing between the free end of the male fitting, where its bore terminates and the free end of the female ferrule where its bore terminates.

Thus there is a gap between the two fittings which cap can be a source of contamination. This can be a considerable problem in the pharmaceutical and food industries, where a contamination-free environment is essential. Everything has to be done to eliminate such causes of contamination.

The present invention is directed towards providing a ferrule which will overcome the problems of existing parallel threaded female ferrules.

Statements of Invention According to the invention there is provided a coupling including a bored parallel threaded female ferrule for mounting on a bored externally tapered threaded male fitting having a predetermined gauge length and fitting allowance for a matching parallel thread and having an end face characterized in that the coupling carries a compressible gasket seal for contacting the end face of the male fitting and in which the length of the female thread is matched to the configuration of the male thread so that its length exceeds the gauge length of the male thread by an amount sufficient to compress the seal and not exceeding the fitting allowance of the thread. The advantage of this is that it can be so designed that there will be no gap between the free end or face of the male fitting where its bore terminates and the free end of the female ferrule where its bore terminates. Ideally the bore of the coupling is configured to accommodate the seal on compression to provide a smooth transition between the two bores. The advantage of this is that a smooth transmission will be provided between the two bores leading to a lack of contamination and a lack of lodging of contaminates in the coupling. Ideally the male fitting has at least ten full threads and not less than 7.5 full threads. The advantage of this is that there will be sufficiently tight coupling.

In one embodiment of the invention the fitting is manufactured to British Standard Specification No. BS21:198-5 and the length of the female thread - 3 is computed by the formula: LF = [d/1.6 + (x - I)] - (4R3) where Lf = length of female thread d = gauge diameter x = thickness of joint sealing ring or gasket 10 r = thread size designation fraction.

I = desired reduction in depth of seal on compression.

In one embodiment of the invention the seal is of a polytetrafluoroethylene and L is 0.5. When the seal is polytetrafluoroethylene it is particularly advantageous to also use a polytetrafluoroethylene tape on the male thread.

Detailed Description of the Invention The invention will be more clearly understood from the following description 20 of an embodiment thereof given by way of example only with reference to the accompanying drawings in which:Fig. 1 is an end view of a ferrule according to the invention; - 4 Fig. 2 is a side sectional view ot the ferrule with the sectional lines omitted for clarity; Fig. 3 is an enlarged view of portion of the ferrule illustrated in fig. 3; and Fig. 4 is a sectional view showing a tapered threaded male pipe connected to the ferrule.

There are many standards, both international and national relating to thread sizes, the configuration of tapered threads on male members and the like. British Standards are used extensively throughout the world. In this specification the terminology of British Standard Specifications and in particular BS21:1985 is used. In this British Standard Specification there is defined a complete thread for an externally threaded male fitting together with an incomplete thread and a wash out thread. There is further defined a gauge length which is defined on an external thread at a distance parallel to the axis from the gauge plane to the small end of the thread and then there is defined a fitting allowance which is made up partially of a portion that will allow hand tight engagement and then a portion of the thread for allowing a fitting having a parallel thread to be mounted thereon by a wrench or other means. All standard specifications have somewhat the same definitions. However, in this specification the definitions used in British Standard Specification are the onesiollowed and thus, if the present invention is to be - 5 applied to other standard specifications then the necessary formula etc. described therein will require modification having regard to these definitions. It will be appreciated that in all cases the gauge length is related to the gauge diameter, that it to say, the basic major diameter of the thread.

Referring now to the drawings, there is illustrated an internally threaded female ferrule, indicated generally by the reference numeral 1, which incorporates a flange 2, details of which are not given as they are irrelevant. The ferrule 1 has an internal stepped bore, namely an inner bore 3 and an outer bore 4. The inner bore 3 has a parallel thread 5 of conventional construction. An annular groove 6 is provided for reception of a special PTFE seal 7 which is only illustrated in Fig. 4. The length of the parallel thread 5 is derived from the formula: Lf = [d/1.6 + (x- l)j - (4R3) where LF = length of female thread d = gauge diameter x = thickness of joint sealing ring or gasket r = thread size designation fraction.

I = desired reduction in depth of seal on compression. - 6 The precise depth LF has been determined by an extensive development programme involving practical and theoretical analysis. The advantage of the invention is that with a ferrule so constructed there is a smooth transition between the bore of the ferrule and the bore of the fitting.

Referring now specifically to Fig. 4 where there is illustrated a fitting namely a male pipe 10 having an external tapered thread 11 on which the ferrule 1 is fitted. It will be noted that the free end of the male pipe 10 bears against the special PTFE seal 7 thus providing a tight seal and while in Fig. 5 the seal is not shown deformed, it would generally deform somewhat to fill the tapered portion of the ferrule.

It will be appreciated that the dimensions and in particular the dimension I will vary depending on the seals and the size of coupling being used. For example, certain practical fittings have been provided in four basic ferrule sizes to suit BS4825 Part 3 1991 fittings, being Vz “, 1” and 1 Vz”. The Vz and 3/4” sizes have a range of % BSP, 1/4” BSP and 3/8” BSP, whilst the 1” and 1 V2” sizes have a range of 1/s”, VS, Vz, VS and 1” BSP. In all cases the BSP threads are tapped to BS21-1985. The seal and fitting internal sizes above are basically the internal diameter of a schedule 40 size pipe. From this internal diameter size the bore is tapered to match the relevant internal diameter of the BS4825 fitting. This gives us smooth transition from one bore to another. The PTFE seal can be replaced if it should become - 7 damaged during use. Then where the fitting is used in connection with a male tapered thread the length of the taper thread is critical to ensure that the PTFE seal is correctly compressed by the pipe. The length of the internal thread can be selected to make this possible but in many instances PTFE thread sealing tape should be used to ensure that a good joint is achieved both against the seal and the threaded system.

It will be appreciated that many forms of elastomeric material and type of 10 gasket or seal may be used, other than a PTFE special seal.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (8)

1. A coupling including a bored parallel threaded female ferrule for mounting on a bored externally tapered threaded male fitting having a 5 predetermined gauge length and fitting allowance for a matching parallel thread and having an end face characterized in that the coupling carries a compressible gasket seal for contacting the end face of the male fitting and in which the length of the female thread is matched to the configuration of the male thread so that its length 10 exceeds the gauge length of the male thread by an amount sufficient to compress the seal and not exceeding the fitting allowance of the thread.

2. A coupling as claimed in claim 1 in which the bore of the coupling is 15 configured to accommodate the seal on compression to provide a smooth transition between the two bores.

3. A coupling as claimed in claim 1 or 2 in which the male fitting has at least 10 full threads.

4. A coupling as claimed in any preceding claim in which the male fitting has at least 7.5 full threads.

5. A coupling as claimed in any preceding claim in which the fitting is - 9 manufactured to British Standard Specification BS21:1985 and the length of the female thread is computed by the formula: L F = [d/1.6 + (x - I)] - (4R 3 ) where L F = length of female thread d = gauge diameter 10 x = thickness of joint sealing ring or gasket r = thread size designation fraction. I = desired reduction in depth of seal on compression.

6. A coupling as claimed in claim 5 in which the seal is a 15 polytetrafluoroethylene (PTFE) and 1 = 0.5.

7. A coupling as claimed in any preceding claim in which a PTFE tape is secured to the male thread. 20

8. A coupling substantially as described herein with reference to and as illustrated in the drawings.