Couplings and BS fittings refer to those fire extinguisher components designed and manufactured in accordance with the standards and requirements of standard BS 336 developed by the British Standardization Institute (BSI). The ease of use and quick couplings are the hallmarks of these couplings, and that’s why they are also called instantaneous couplings.
Figure 1: BS couplings
As noted, the BS couplings, due to their rapid opening and closing, are widely used in firefighting departments, and also due to the mechanism of operation of the water supply connections, which are described in detail below, are very suitable for high-pressure inputs.
In these couplings, the base of connections is the plungers that are embedded in the design of the female connectors and consist of three main sections: bunches, tabs and springs. As shown in Fig. 2, when connecting, by passing the semi male, the tab is first pushed back and returned to its original position with a solid steel spring pressure. At the time of separation, the stretching of two plungers with a force between 45-65 newton leads to the release of the coupling from the back of the tab and opens the coupling. It should be noted that, in the type of single-plunger female connectors, the separation operation is performed with a half-turn of plunger. (Figure 3)
The sealing mechanism of the couplings is connected directly to the design and operation of a special rubber gasket/washer embedded in the female part. Due to the pressure of the water entering the coupling, the conical part of these washers is attached to the body of the male part and sealed without any leakage. Therefore, attention to the material hardness in producing these gaskets/washers is very important and considered as an effective component in coupling performance. High hardness, especially at low pressures, prevents proper sealing, and low hardness also results in the gasket to come out of its place and even may be torn.
Figure 4: Washer gasket
The type of alloy is used and the process of producing BS couplings varies according to the working environment and type of fluid flow. Based on the recommended materials in BS 336, mainly aluminum alloys are used with normal water and copper base alloys are used when the water contains salt and other corrosive salts. Nevertheless, attention to the climate and the type of use on the one hand and the sensitivity and importance of the consumer base on the other hand, is the main factor in choosing the optimal materials. For example, the oil industry and its dependent industrial environments always have a high degree of sensitivity and importance in this regard - especially in our country, in view of the major deployment of oil sites in the vicinity of corrosive marine environments and the use of salt water. Entering this field requires very precise scientific and functional studies. Depending on the type of material used, the process for the production of components is defined, which mainly includes casting, forging and precise CNC machining. It should be noted that any qualitative weakness in the type of material used or the selection of process and inappropriate equipment, directly effects in the quality, test results and, ultimately, the performance of this important products and will lead to an adverse and undesirable result.
The inspection process during and after the manufacturing, in terms of dimensional, metallurgical and mechanical, due to the high sensitivity of the parts, should be carefully executed. Due to the presence of fluid in the circuit, the hydrostatic pressure test is required in accordance with the BS 336 standard for all BS couplings. This test is carried out 24 times and lasts for 2 minutes, and the components are leak tested completely. No leakage at this level of pressure is acceptable. In this regard, the operating conditions can be effective, and before taking any action, the input pressure of the target base should be controlled precisely. Typically, major manufacturers consider the higher limits of maximum standard pressure for hydrostatic testing in order to maximize market coverage in designing and selecting materials.
Another feature of this group of couplings is their resistance to hits caused by collisions during the firefighting process, such as dropping on the ground. Although it is not referred in BS 336 standard to apply mechanical tests, manufacturers have to continuously measure and determine the strength and resistance of the parts, which are influenced by the type of material selected and the quality of the production process, to ensure that the fittings are fitted properly in the event of fire.
Also, since these pieces are not being used continuously, it must be considered in designing these components that the passage of time should not change the quality of its performance - for example, preventing the entry of ambient dust into the earrings with a suitable cap. Also the need for periodic inspections and the development of maintenance and maintenance programs by consumers is inevitable. In this regard, manufacturers should also be able to check the ease of opening and closing of parts periodically without reducing operational sensitivities for the operator and include it in their design.
Figure 5: Arya Brass Cover to prevent dust entering with special service and maintenance wrenches.