taco Sentry

Snowmelt

I was at a customers home wanting the boiler re-piped, the existing zone valves weren't in one area, in fact one zone valve was 15 feet away from the boiler. When the boiler was replaced the contractor didn't update any of the boiler near boiler piping, still has an old air scoop and original zone valves. I am going to replace the air scoop with the taco 4900. The old zone valves are white rogers, I want to replace them with the zone sentry valves. The sales rep told me the 3/4 cv is greater then the 1 inch ( the 3/4 is 10.3 and the one inch is 8.7) with that being said, why use the 1 inch and not just use the 3/4 and on the end of the zone valves just install 3/4 to one inch adapter.

GroundUp

Is 8.7 not enough?

hot_rod

7 gpm is about 4 fps velocity in a 3/4" tube, that is about the max you would want to flow, to keep it quiet and troublefree.

7 gpm thru a 10.3 Cv valve is .46 psi pressure drop.

Snowmelt

That one zone ( main house is 1 1/4 piping) but I’m almost positive it’s over sized pipe so if the zone with the 1 1/4 piping is only 80,000 btu or closer to an even 100,000 btu could I just use the 3/4 inch sentry valve and a one inch to 3/4 reducer and squeeze the 100,000 btu thru the zone valve?

newagedawn

no, not a good piping practice but its your life

Zman

Sizing the valve to the designed flow rate and resistance is the right way to do it. If you had an old 3" gravity pipe, you sure wouldn't go find a 3" valve for the application.
I would absolutely stay under 4 ft/sec if the valve is in an area where velocity noise will be a problem. If it is just going in a boiler room, 6 ft/sec is OK as long as it is within the manufactures recommendation.

hot_rod

I agree with Zman , any/ all valves should be sized by the intended flow rate and acceptable pressure drop. Notice that valves are often available with various Cv ratings. We build 3/4 spring return zone valves in 2.5, 3.5, 5 and 7.5 Cv.

Be especially careful with check valves and flow checks, their Cv rating is in the full open position. If you oversize, the flapper or disc inside is floating around somewhere between full open and full close position. Noise, wear, and additional pressure drop is the result.

While it may look odd you may see a 1-1/4 check valve on a 2' pipe for example, that is fine if it was sized properly to the actual flow rate.

Check valve sizing is becoming even more critical with variable speed pumping. Use a check designed for hydronics so they pop open and are friendly to flow in partial open positions.