Angle Seat & Globe Valves
If we consider the relative surface inside a globe valve which is subjected to pressure, it becomes clear that this functional principle is particularly suited for use with high operating pressures. It is generally known that force is the result of pressure times surface area. If the flow direction is changed in a globe valve, the force ratio is altered in the opposite way than is the case in the butterfly, ball or diaphragm valve.
This is important in as far as it can be used to influence an unfavorable closing and operating pressure force situation. In the case of electromagnetically actuated globe valves, the flow direction must always be effected with the disc due to their low closing forces. Sealing is effected with the aid of a wide variety of sealing materials, but a so-called "steel on steel" seal is also possible. This involves both a steel globe and a steel plate, which are so precisely machined that a complete seal is achieved under the closing force of the actuation system. The spindle is normally sealed using shaped plastic sealing rings which act, depending on their installation and pretension direction, as pressure, vacuum, or combination seals.
When a high level of temperature resistance is necessary, this type of plastic seal is replaced by a metal bellow. This results in temperature resistance of at least +300° C. Some manufacturers offer variations resistant to even higher temperatures.
However, insertion of a metal bellow serves to restrict the stroke. When determining the volumetric flow (KV value), therefore, attention should always be paid to select the next highest nominal width.
In a globe valve, the medium is subjected to marked deflection. This can be improved by using an angle seat globe.
Globe valves are found in applications ranging from the smallest nominal widths up to 150 mm (6") and even higher involving medium to high operating pressures and temperatures. Fitted with a relatively "hard" seal and due to the rigorous medium guidance, globe valves are usually insensitive to soiling. This functional principle, however, should be used with caution where abrasive media are being transported.
The control properties can be positively influenced by the relatively long stroke, the shape of the globe and also the use of a control taper instead of a disc to the extent that optimum control characteristics can be achieved. The globe valve can therefore be designated the standard control valve.
- Water treatment
- Installation construction
- Irrigation systems
- Inert and corrosive liquids and gases