The valve plug is therefore able to reproduce small changes in flowrate, and should not be regarded as a fast opening control valve. The movement of this type of valve plug can be extremely small relative to small changes in the controlled condition, and consequently the valve has an inherently high rangeability. The plug position responds to changes in liquid or vapour pressure in the control system. The self-acting type of control valve tends to have a plug shape similar to the fast opening plug in Figure 6.5.1. Therefore, two valves, one giving a 80% flow for 50% lift, the other 90% flow for 60% lift, may both be regarded as having a fast opening characteristic.įast opening valves tend to be electrically or pneumatically actuated and used for ‘on/off’ control. Unlike linear and equal percentage characteristics, the exact shape of the fast opening curve is not defined in standards. For example, a valve lift of 50% may result in an orifice pass area and flowrate up to 90% of its maximum potential.Ī valve using this type of plug is sometimes referred to as having an ‘on/off’ characteristic. The fast opening characteristic valve plug will give a large change in flowrate for a small valve lift from the closed position. The inherent flow characteristics of typical globe valves and rotary valves are compared in Figure 6.5.2.Įxamples of these and their inherent characteristics are shown in Figures 6.5.1 and 6.5.2. Rotary valves (for example, ball and butterfly) each have a basic characteristic curve, but altering the details of the ball or butterfly plug may modify this. In this Module, the term ‘valve lift’ is used to define valve opening, whether the valve is a globe valve (up and down movement of the plug relative to the seat) or a rotary valve (lateral movement of the plug relative to the seat). Typical trim shapes for spindle operated globe valves are compared in Figure 6.5.1. The physical shape of the plug and seat arrangement, sometimes referred to as the valve ‘trim’, causes the difference in valve opening between these valves.
Comparing linear and equal percentage valves, a linear valve might have a 25% valve opening for a certain pressure drop and flowrate, whilst an equal percentage valve might have a 65% valve opening for exactly the same conditions. However, different valve characteristics will give different ‘valve openings’ for the same pass area. Valves of any size or inherent flow characteristic which are subjected to the same volumetric flowrate and differential pressure will have exactly the same orifice pass area. For any valve, however it is characterised, the relationship between flowrate and orifice pass area is always directly proportional. The orifice pass area is sometimes called the ‘valve throat’ and is the narrowest point between the valve plug and seat through which the fluid passes at any time. It does not refer to the orifice pass area. Please note that ‘valve opening’ in this context refers to the relative position of the valve plug to its closed position against the valve seat. Simple adjustment to new parameters and requirements thanks to functional modules and graphical configuration.All control valves have an inherent flow characteristic that defines the relationship between ‘valve opening’ and flowrate under constant pressure conditions.
Redundancy layout for fire detection and selection of multi-zone extinguishing systems.Freely programmable graphical controls that meet common requirements in terms of displaying alerts and executing commands in a chosen logical and chronological order.Up to 32 control panels and parallel indicator panels – can be linked redundantly to a ring network.Detector operation in industrial environments and fire characteristics such as heat, smoke, flames and CO combustion gas, linkable to the detector loop.Ring bus technology featuring a comprehensive range of cutting-edge characteristics to facilitate notifying, controlling and monitoring – even in explosion hazard areas.A large graphical display with ergonomic menu based user interface for clear alerts and ease of use in every situation.All FMZ 5000 models combine innovative functionality with state of the art fire detection and extinguishing control panels in a single unit–which, of course, can be part of a network.
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