You might think when selecting a master mixing valve, that you can’t go wrong by going big.
However, we strongly advises against that philosophy. While oversizing isn’t the major issue it once was due to the outstanding low flow performance of the ConTrols® MV17 master mixing valve, an oversized valve costs more—sometimes a lot more. Repair parts will be more expensive, and you will spend more time replacing them.
Even if you feel you’ve never had a problem when you’ve gone big, you are in fact forfeiting some level of low-flow performance possibly to the extent that it will make a difference in bather comfort—or worse, bather safety. The larger valve may need servicing sooner because its sensor has to work harder dealing with flow rates that are better suited to a smaller valve. Not to mention the damage to your reputation should the building owner discover that a smaller valve would have met their needs without having to deal with all the above issues.
The only way to size your master mixing valve is to perform calculations using site and design data and then, use a valve’s flow coefficient, or Cv, to select the right valve. This will save you money and a few headaches in the long run.
The flow rate through a master mixing valve depends on a higher inlet pressure than outlet pressure, no matter how small or large, and is measured in pounds per square inch differential (PSID). We also like to call it “available system pressure differential.”
The well-intended but misplaced belief that you need to minimize loss through the valve has led design engineers to oversize their valve selection for their application. If you call it “loss (or drop) through the valve”—acceptable jargon for most mixing valve manufacturers—it could imply that you believe the valve should be sized based on the pressure you can afford to lose through it at peak demand.
To size your mixing valve correctly you need to know these key data points:
- Type of project
- Master mixer setpoint temp
- Minimum CW temp
- Fixture outlet temp
- Inlet pressure at the valve
- Height of riser to farthest fixture
- Horizontal distance from riser to farthest fixture
- Usage factor (if the number of fixture units per Hunter’s curve is less than 50)
- Fixture count
- Hunter’s curve fixtures units
- Cv (flow coefficient) required to meet peak demand
- GPM required for peak demand, based on Hunter’s curve
Only with this information in hand can you calculate the proper size for your mixing valve. The good news is, we’ve taken care of the tedious part and created a calculator to run the numbers for you! All you need to do is plug in the data. It’s even mobile-friendly so you can use it right on the job site.
However, for our representatives wanting to understand the magic behind our master mixing valve calculator, you can download a guide (restricted access). This guide details the steps taken to size a valve correctly using the example of a nursing home.
To download the guide simply use the Rep Login area on the MGO site and look for the guide under *Downloads >> Sales Support and Contacts or under Downloads >> Tools and Calculators.
If you have questions or would like more information on any ConTrols products, please contact us.