An automatic recirculation valve refers to a multifunctional valve which is majorly used to ensure a specific minimal flow is assured through a centrifugal pump every time. This is essential because a centrifugal pump suffers from cavitation and overheating and can be damaged permanently if they run dry. The abbreviation of Automatic Recirculation Control valve is ARC, this is a registered name and the function of the valve is the same as the AR valve.
The major part which will be sensitive to the flow is the heart of the recirculation valve which is sensitive to flow and not sensitive to pressure. The disc will ensure the process flow and alsoen sure a minimum flow via the pump. This attributes will lead to a stable, consistent as well as performance which will be repeated over a range of pressure.
1. Immediately the disc is at full capacity, the bypass will be closed and once the process flow decrease, the action will be reversed and there would be an increase in the flow rate. The flow would go into the bypass element which is located at the bottom of the disc assembly and is controlled by the orifices which is inside the disc stem. The flow then continues via an annulus before it would be directed to the valve outlet. Such valve would make provision for one flow path in that bypass, and would eliminate the chance of cavitation or flashing. This is attained by the design of the valve and the regulator of external back pressure can be used if necessary.
2. Immediately the disc lifts when reacting to the increase in the flow to the process, the element of the bypass which is essential to the disc would close the bypass so as to limit the recirculation flow. The disc position will control the recirculation flow. This feature would ensure that the entire process flow as well as recirculation flow is higher than the lowest flow via the pump according to the manufacturer’s specification.
3. When the disc is in closed position, the bypass will be fully open and there won’t be any process flow. This will help in protecting the pump against accidental or planned dead heading which can occur as a result of closed down stream pump isolated valve or process control valve.
The best thing is to install the automatic recirculation valves directly on the outer part of the pump for which they are meant. The layout of the valve is majorly based on the pump curve. Make sure the valves are installed on the appropriate pumps. The direction of flow is indicated on the valve nameplate. This nameplate is inscribed on the body of the valve. The valve fabricating number would also be found on the nameplate. This is a unique number and different for each valve. This will ensure that the valves can always be used with the right pump and this number should be used if there is any need to get a spare part.
The valves are usually supplied together as a whole unit and can be installed directly after the receipt. Normally, the connections are flanged but the valves with butt weld ends can be supplied upon request. The packaging which is needed between the valves as well as the piping is not part of our scope of supply but this packing can be supplied as an option. This is also the case with the bolts and nuts. Based on the weight of the valves as well as the position of installation, the valves can be installed by hand or with the aid of a tackle.
Before the installation of the valve, you need to ensure that the system does not have pressure. The pumps must be switched off and the lines must be drained and clean. The isolating valves should be closed so as to prevent any form of backflow from other tanks or lines. The flange covers of the valves must be removed before the installation. Ensure that there is no foreign material in the valve after removing the covers. If you want to install the valve after installing it over a long period of time, you should check them on possible rust and clean them if necessary.
You can lift the valve by hand or with the aid of a tackle on top of the pump outlet flange. Ensure that the right flange packing is correctly positioned between the valve inlet flange and the pump outlet flange.
The lifting strap can be slung around the valve outlet flange, ensure you do not use the bypass flanges to lift the valve. The flange bolts should be tightened crosswise. You can then connect the flange of the main process line to the valve outlet.
It is more practical to use two different straps in case of horizontal installation, one around each main flange so as to position the valve in front of the pump outlet flanges. Once this is done, you can then connect the pump as well as the piping as earlier described.
There is need to orientate the valve bypass connection in a horizontal or vertical position so as to prevent the settlement of possible dirt on the moving parts of the valve. The bypass connection of the valve should not be installed in a vertical upward position. The weight of the check valve would tend to pull it out of its seat.
It is always challenging to install the valve directly on the outlet of the pump. In this kind of scenario, the distance between the outlet of the pump and valve inlet in less than 1.5 meter the inlet can be connected directly to the piping which is coming from the pump. If the distance is bigger the location must be planned so as to indicate in case of order so that the design can be taken into consideration. The valves which are ordered for the horizontal installation should not be installed vertically and vice versa without consulting the manufacturer because each has been designed for a particular purpose.
For valves which have welding connection, it is essential to check the dimension as well as material which are selected for the whole connections before they are being installed. Check whether the weld edges are not damaged.
Depending on the kind of connection which was provided, the valves are supplied with welded connection directly into the pipeline. The bypass connection is always flanged, when valves with weld connection. There is need to take special care because hoist-straps cannot be hooked around a flange and exact positioning is needed for the welding work. Once the valves are installed, the system can be pressurized so as to check any leakage and the maximum test pressure based on the pressure rating of the valves as well as the material used.