# Valves

If you intend modelling the effects of changing the % opening of a two-port valve in a system, we need to ensure that the flow vs. pressure loss data for the valve has been defined in the database. Many valves in the database have the flow vs. pressure loss defined. This relationship can be defined by: 1) K with positioning, 2) Kf with positioning or 3) Cv,Kv with positioning. If a valve has been defined in the database by: 1) K no positioning, 2) Kf no positioning and 3) Cv-usgpm/psi no positioning, 4) Kv-m3/h/kPa no positioning or 5) Kv-l/min/bar no positioning, we will not be able to model changes in the % opening of the valve from the Input Inspector. Figure 1 below provides an overview of how a valves flow vs. pressure loss relationship may be defined in FluidFlow. Figure 1: Two-Port Valve Flow vs. Pressure Loss Definition. Fire Hydrants. The FluidFlow Valves Database contains two hydrant types: 1) Typical Free Flowing & 2) Recordall Turbo 450. The "Typical Free Flowing" hydrant has its pressure loss characteristic defined as "K no positioning". This simply allows one characteristic value to be entered for the valve, in this case 4.5 bar g, at 100% open. For further information select: Database | Valves | Fire Hydrant | Typical Free Flowing. Fire hydrants are usually operated in the fully open position and there is usually a downstream resistance such as a flexible hose and nozzle. If you wish to operate in a throttled position then you need to enter further data for the hydrant to the database. The "Recordall Turbo 450" fire hydrant has its pressure loss characteristic defined as Cv,Kv with positioning. This therefore means we can model this valve and throttle the valve opening position in which case, we will get lowering of flow through the valve with progressive throttling of the valve position. Design Note: Fire hydrant systems may be modeled with Known Pressure boundary nodes at each outlet point which means we can define the back-pressure for each hydrant in the system. This will allow you to increase the back-pressure downstream of the hydrant using a "trial and error" approach. This will then give you the design flow and the maximum back pressure of any fire fighting equipment downstream of the hydrant. You can also add you own specific hydrant to the database by selecting: Database | Valves and Select "Fire Hydrant" followed by "Add". This will enable you to model your specific hydrant in the system. Size Mismatch Warning This warning will be enunciated when the inside pipe diameter connecting to a given valve doesn't match the valve diameter as defined in the database. You can overcome this warning by selecting a different pipe diameter or inserting reducers into the connecting lines.