Valves need to be sized appropriately in accordance via the mechanism needs to ensure appropriate and also steady operation throughout the complete array of flows required for refrigeration loading and also condenser water temperature problems. Appropriate sizing is determined by maximum compelled condenser water circulation price and also easily accessible press drop (accessible press to press the water via the valve). The adhering to actions need to be taken in sizing and also selecting a valve for normal installations:
1. Determine the water flow required at maximum pack problems.
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The maximum water flow is normally specified by the condenser manufacturer. If this information is not readily accessible, an excellent "rule of thumb" is 3 GPM water per ton of rated refrigeration capacity, assuming 85°F maximum tower water conditions. If the water temperatures vary significantly from these numbers gave, a typical value"s required water circulation have the right to be calculated as follows:
2. Determine the push drop available for the valve. The value should be schosen to carry out forced maximum rated flow at a press drop that is acceptably low in comparikid the pressure drop that is accessible from the device.
The accessible push drop can be described primarily as the Supply Prescertain, minus the Sum of the Prescertain Losses in between the Supply and also Rerevolve sources, minus the Return (to tower) Pressure at rated maximum flow. Important note: all pressures and also push drops have to be figured out or calculated at rated maximum flow. Specifically:The Supply Prescertain is taken from the outlet of the pump giving the water or from the water supply press.Subtract the press drop in the Condenser at the rated water flow, typically accessible as component of the chiller specification.Subtract line losses as a result of fittings, long runs, strainers, and so on., typically a low value between 2 and also 5 PSI unmuch less tbelow are long runs, high line velocities or many kind of fittings.Subtract the Rerevolve Pressure in the line to the cooling tower from the same elevation as the Supply Pressure.Multiply the outcome by a safety element, normally between .75 and also .85
3. Select the correct flow capacity value by calculating the circulation coefficient (Cv) required making use of the complying with formula:
The preceding sizing consideration is for "normal" applications. For applications having extreme operating conditions such as extensively varying water temperature, inexplicable press differentials, and so on, a Metrex application engineer should be consulted.
It is vital to prevent over-sizing valves. A properly schosen valve is sized to be totally open or nearly fully open throughout conditions wbelow maximum circulation is required. Remember it is the valve"s project to provide control by restricting the circulation of water as forced through a broad variety of varying mechanism conditions including fill, condenser water temperature and also obtainable mechanism pressure. Although Metrex valves are engineered to run successfully through the widest array of any kind of valve of this type, control valves of this nature execute not run well at the excessive low end of their operating selection if sized too huge.
Additional, it have to be listed that pilot valves require a minimum pressure drop to attain correct procedure. Consult individual Valve Data Sheets for a conversation of minimum requirements.
Following these actions carefully will certainly ensure optimal valve sizing resulting in trustworthy and effective device regulate. If any kind of concerns aclimb in valve application or sizing, carry out not hesitate to call one of our application engineers.
Remember: it is our goal to carry out "Set and also Forobtain Relicapability." SIZING EXAMPLE 1
1. Deauthorize Condenser Flow (from chiller manufacturer) = 100 GPM
2. Available Prescertain Drop:
Pump Supply Pressure:
Rerotate to Cooling Tower:
Available Pressure =
Determine Flow Coefficient:
In this example, the desired valve have to have a Flow Coefficient of at least 23.
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The Metrex 2-1/2" 2-Way 800P Series via a Cv of 26 (slightly larger than required) will work-related well for this application.