GB2106616A

GB2106616A - Flow restrictor and safety device for gas cylinders

Info

Publication number: GB2106616A
Application number: GB08226081A
Authority: GB
Inventors: Joel Blondet; Jacques Henry
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1981-09-14
Filing date: 1982-09-13
Publication date: 1983-04-13
Also published as: BE894389A; GB2106616B; DK408282A; ES277887U; CH650851A5; IT8268085A0; MA19588A1; FR2515301A1; FR2515301B1; IT1156524B; ES277887Y; IT8253676V0

Abstract

The invention relates to a flow restrictor 10 for gas cylinders, comprising a blind tube made of flexible material, provided at its closed end 14 with a splayed slot (12, Fig. 1, not shown) in communication with the inner passage of the blind tube and to be fitted at its open end into the valve inlet (11) of a gas cylinder. The restrictor further comprises at least one rib 18 enabling the flow restrictor to be rotated by a mounting implement 32. These ribs 18 also alow the torque load to be restricted in that they will yield above a certain value; finally when the ribs reach the level of the bottom of the valve inlet, this indicates that the restrictor is screwed fully into the valve. <IMAGE>

Description

SPECIFICATION Flow restrictor and safety device for gas cylinders This invention relates to a flow restrictor for gas cylinders, in particular for cylinders containing liquefied petroleum gases, and to a safety device for gas cylinders comprising a valve and a flow restrictor. The flow restrictor serves to prevent too high a gas flow rate should the valve be left open after disconnection of the tube, should the tube rupture or should the valve inlet break off at the level of the neck of the cylinder, for example due to dropping the cylinder.

French patent specification No. 1,184,318 describes such a flow restrictor comprising a blind tube made of flexible material fitted at its open end, for example by screwing, into the valve inlet, and comprising at its closed end a splayed slot, such that, in the event of excessive discharge, the deformation of the material causes the lips of the splayed slot to come together, thus reducing the discharge of gas to the outside.

These flow restrictors have now been in use for nearlytwenty-five years, during which time they have performed an essential safety function and have proved completely adequate, provided that they are positioned correctly in the valve inlet. In fact, these flow restrictors are usually assembled by screwing, and if this is inadequate, or if the threads are affected, the flow restrictor may be ejected from the valve inlet during filling of the cylinder. This risk becomes greater at higher filling rates, when the increase in the flow velocity of the liquefied petroleum gas creates higher stresses, due to the pressure difference across the blind tube.

In French patent application No. 7607454 (published under No. 2,344,770), an attempt was made to remedy this problem by means of a reinforcing ring which would hold the open end radially in contact with the thread pitch of the valve inlet.

Although the device unquestionably improves the anchorage of the flow restrictor in the valve inlet, it in no way prevents incorrect positioning of the flow restrictor. As the latter is made from flexible material, it is not unusual that the threads are affected, for example if the two parts to be screwed together are misaligned, in which case the valve inlet and the flow restrictor are interlocked, but the connection between the valve inlet and the flow restrictorwill not withstand the stresses to which it is subject during filling.

Furthermore, even if centring is correct, under- or over-tightening will weaken the resistance to ejection. In the first case, as the flow restrictor is not in contact with the bottom of the valve inlet, the threads ef the flow restrictor are not in a state of compression and the connection is weakened. In the case of over-tightening, however, there is a danger of deformation of the threads of the flow restrictor and imperfect contact with the screw thread. There is also a danger that the flap may break, because this bears most of the stress of screwing, as will be seen below.

To resolve all these problems, the invention proposes a flow restrictor of the aforesaid type but with the addition of at least one rib on the outer surface of the blind tube, enabling the flow restrictor to be rotated by a mounting implement. Preferably, this rib is a straight, longitudinal ridge running parallel to the axis of the blind tube, and with a shape and dimensions such that the elastic deformation resulting from a given value ofthetorque load of the mounting implement enables the rib to be liberated from the action of the mounting implement. Finally the length of the rib is such that it reaches the level of the bottom of the valve inlet when the flow restrictor is screwed fully into the valve inlet; it is thus easy for the operator to ascertain that the flow restrictor is screwed in to the correct depth.

By performing this triple function of allowing the flow restrictorto be rotated, restricting torque load by yielding when a certain value is reached and providing indication that screwing is complete, these ribs offer a simple means of resolving the difficulties previously encountered and ensuring that the restrictor is always correctly assembled.

The invention will now be described byway of example in more detail with reference to the drawings, wherein: - Figure lisa perspective view of the flow restrictor according to the invention, mounted in a valve inlet; - Figure 2 is a cross-section of the flow restrictor according to the invention at the level of the ridges; - Figure 3 is a vertical section of a prior art flow restrictor in its mounting implement before introduction in the valve inlet; and - Figure 4 is the same view as Figure 3 for the flow restrictor according to the invention.

Reference is first made to Figure 1 showing the flow restrictor according to the invention, referred to with numeral 10, mounted in a valve inlet 20. The flow restrictor 10 comprises a blind tube made of flexible material of which the open end 11 is in communication with the bore 21 of the valve inlet 20.

At the closed end of the blind tube a splayed slot 12 is located, such that, in the event of excessive discharge, the deformation of the flexible material causes the lips of the splayed slot 12 to come together, thus preventing too high a flow of liquid.

The blind end is further provided with a bevelled part 13, which increases the flexibility of the flap 14, as the narrow area 15 forms a hinge. The flow restrictor 10 is attached to the valve inlet 20 by a threaded section 16 which fits into the thread in the bore 21 of the valve inlet 20. In an alternative embodiment, the flow restrictor 10 has an unthreaded section 17 which will fit in an unthreaded section in the bore preceding the thread of the valve inlet; this facilitates the alignment of the flow restrictor 10 in the valve inlet 20 when the restrictor is being mounted.

According to the invention, the flow restrictor 10 further comprises one or more ribs 18 mounted on the outer surface of the blind tube, which have been represented in the form of rectinlinear, longitudinal ridges; in the cross-section in Figure 2, two such ridges can be seen with a roughly semi-circular cross-section. However, the number and shape are by no means limitative; it is sufficient that the flow restrictor has reliefs on its outer surface which, regardless of their shape, allow the flow restrictorto be rotated by a suitable mounting implement, and whose arrangement and size are such that the elastic deformation of these reliefs allows the flow restrictor to be liberated from the action of the mounting implement. Over-tightening is thus prevented.

Furthermore, the length of the ribs is such that their upper ends 19 reach the level of the bottom 22 of the valve inlet 20 when the flow restrictor 10 is fully screwed in; the operator installing the flow restrictor can thus check that the flow restrictor is screwed in far enough.

From Figures 3 and 4 it can be seen that this invention reduces the risk of breaking the flap. In previous designs (see Figure 3), a flow restrictor 24 was rotated by a mounting implement 30 with a sloping area 31 corresponding to the bevelled section 25 of the flow restrictor 24, the dimensions of the mounting implement 30 being such that the flow restrictor was rotated by friction on its lower part.

With this arrangement it can be seen that there was a danger that over-tightening would break the flap 26 at the hinge 27, or at least exert a pressure in excess of the limit of elastic deformation, thus damaging the flow restrictor.

However, a mounting implement 32 which exerts no stess on the flap 14 of the flow restrictor 10 can now be used (see Figure 4). The mounting implement 32 comprises a cylindrical bore with for example grooves 33 having sections corresponding to those of the ridges 18 of the flow restrictor 10, or with any other section allowing rotation and the restriction of torque due to the elasticity of the ridges 18 which causes them to yield. It therefore becomes impossible to damage the flap 14 of the flow restrictor according to the invention on assembly.

The invention is naturally not limited to the embodiment described, and many variations with regard to the number, shape and size of the ridges may be envisaged within the scope of the invention.

Claims

1. Flow restrictor for gas cylinders, comprising a blind tube made of flexible material, provided at its closed end with a splayed slot in communication with the inner passage of the blind tube and to be fitted at its open end into the valve inlet of a gas cylinder, characterized in that it comprises on the outer surface of the blind tube at least one rib enabling the flow restrictor to be rotated by a mounting implement.

2. Flow restrictor as claimed in claim 1, characterized in thatthe rib has roughly the shape of a rectinlinear, longitudinal ridge running parallel to the axis of the blind tube.

3. Flow restrictor as claimed in claim 1 or 2, characterized in that the rib has a shape and dimensions such that the elastic deformation resulting from a given value of the torque load of a mounting implement enables the rib to be liberated from the action of the mounting implement.

4. Safety device for gas cylinders comprising a valve and a flow restrictor as claimed in any one of claims 1 to 3 which can be assembled by screwing into the valve inlet of the valve, characterized in that when the flow restrictor is screwed fully into the valve inlet, the end of the rib is at the level of the bottom of the valve inlet.

5. Safety device for gas cylinders comprising a valve and a flow restrictor as claimed in any one of claims 1 to 3, which can be assembled by screwing into the valve inlet of the valve, characterized in that the valve inlet comprises an unthreaded section preceding the thread of the valve inlet, and into which the flow restrictor fits when the flow restrictor is mounted in the valve inlet.