Taco sentry zone valves

Snowmelt

If a 3/4 sentry is 10.3 cv
& a 1 inch sentry is 8.9 cv
Does that dictate that the 3/4 will have a better flow rate then the 1 inch.
Ex. If I had a 1 inch pipe going to an indirect water heater and I wanted to use a zone valve ( which I don’t but for this example) and I wanted the greater gpm of the two zone valves. The 1 inch pipe to assure I will get close to 10 gpm which is 100,000 btu. The question is will the cv rating of the 1 inch slow the water so I should use the 3/4.
Bear with the long explanation but I am getting different answers from my supply house.

hot_rod

Short answer, yes.

Those Cv are not all that far apart, basically a 9 and 10Cv if you round. Assuming the original flow test to rate the valves was accurate

Cv is the gallons per minute that will flow thru the valve with a 1 psi pressure drop.

So pick a flow rate, use 12 gpm, that is typically accepted max, flow rate (4fps) for 1" copper in hydronic applications.

Here is what that would look like in an actual 12 gpm flow condition.

I doubt your circulator would even feel the difference.

Snowmelt

thanks hot rod, let ask I went to a house because a zone valves wasn't working, it looked like a spaghetti mess. he wants me to replace all 3 or 4 zone valves. (1 zone valve is for the indirect water heater.) The question came about because one zone has 1-1/4 pipe but after doing my heat loss, the btu where 65,000 btu which 1 inch pipe would be good. so when I was talking to the taco rep he scared me when saying the 1 inch sentery was less then the 3/4. in my mind I was going to instill the 1 inch and just put 1 to 1 1/4 adapters .
so I was going to use 2 3/4 for the smaller zone and a1 inch for the bigger zone and a 007 for the indirect.
(his is what I been blabbing about for past week.

hot_rod

I'm curious what the 1" valve has a lower Cv? Does it have flow restrictive tailpipes or something? You are not the first to come here with the question about the Cv of that valve. Maybe they should rate them the same and lessen the confusion

I wouldn't sweat the difference between Cv's that close to one another in that application, if 6.6 gpm is your intended flow rate.

Most any common 3/4 zone valve on the market would handle up to 10 gpm without excessive flow restriction.
But do confirm the Cv on the valve, there are some low Cv valves designed for high pressure shutoff. Sometimes suppliers mis-order and end up with 1 or 3 Cv valves on the shelf.

6- 7 gpm isn't a problem for 3/4 copper, at 6.6 gpm 4 fps velocity in 3/4" no harm in upsizing to 1"

Ideally analyze the entire indirect loop, coil, piping, fittings, valves and determine a pressure drop. Then assure the circulator can meet that load at the gpm you want to send it's way.

I'd spend more time on that and less arguing about a 9 or 10 Cv valve with the supplier Good for you trying to determine the relationship and best application.

GroundUp

@hot rod what is the conversion equation for Cv/pressure drop or what software were you using above? I've never been able to figure out the equation

hot_rod

it's an Excel that Mike our engineer in Milwaukee built.

Let me see if I can attach. Let me know if it downloads.

if you have any two factors you can serve the 3 rd.

GroundUp

That does load, awesome. Thank you!

Joe Mattiello

The standard zone sentry is a reduced port ball valve that uses the same internals for the ¾” and 1” valves.
The flow in the 1” pipe has a greater restriction then the flow in the ¾”pipe when passing through the valve.
Greater restriction causes higher pressure drop across the valve.
This affects the resultant Cv .
Cv=Q/sqrt Delta P
Q= flow in GPM
Delta P- pressure drop in psi
hopefully, this helps

Snowmelt

OK I follow what your saying, t he question to the taco service engineer would be why would i INSTALL a 1 inch product when the 3/4 does the same job? please give me an example

Solid_Fuel_Man

I think you'll find several manufacturers who do this same "sharing". Basically the 1 inch version is just the same as a 3/4 but with 1" connections. Caleffi's Z-one is like that as well. Both the 3/4 and 1" have a CV of 7.5 and have the same EPDM paddle, basically just saves you from using 1x3/4 adapters and looking wonky. But flow wise it makes little difference.

As a side note, flowing over the CV rating is not ingerrantly bad, it just causes more than 1psi pressure drop across the valve. That just needs to be figured into the head calc.

GroundUp

It doesn't do the same job, because 1" pipe will carry more BTU than 3/4" pipe regardless of the pressure drop across the valve.

100 ft of 3/4" Type L at 8 GPM (which is 5.9 FPS velocity, too fast) has a head loss of 6.9 PSI; add in the .6 drop for the valve at 10.3 CV you have 7.5 PSI or 17.325 ft of head.

100 ft of 1" Type L will have only a 1.9 PSI head loss at the same 8 GPM (with only a 3.3 FPS velocity, which is decent) so we have a .81 PSI drop across the valve at 8.9 CV which is more, but when added to the 1.9 in the pipe, it's still only 2.71 PSI total loss or 6.26 ft of head.

So using the 3/4" valve in an otherwise 1" system would lower your drop across the valve from .81 to .60, but that translates to only .4851 ft of head. Is that worth soldering or screwing in a pair of reducers for 6" of head?

I just did this math now so please excuse me if it is incorrect. I am seeing it does not actually match up seeing as the reduced port is identical between the two (shouldn't drop across it also be the same?)

Solid_Fuel_Man

I was thinking they should be the same as well, if the port is the same.

I know Caleffi sells their valves by CV.

hot_rod

Solid_Fuel_Man said:

I think you'll find several manufacturers who do this same "sharing". Basically the 1 inch version is just the same as a 3/4 but with 1" connections. Caleffi's Z-one is like that as well. Both the 3/4 and 1" have a CV of 7.5 and have the same EPDM paddle, basically just saves you from using 1x3/4 adapters and looking wonky. But flow wise it makes little difference.



As a side note, flowing over the CV rating is not ingerrantly bad, it just causes more than 1psi pressure drop across the valve. That just needs to be figured into the head calc.

Correct you are, Caleffi offers a 3/4, 1, & 1-1/4 zone valve, 7.5 Cv Same internals, just different connection diameter in the body.

In fact to build our 1, 2.5, 3.5 and 5 Cv valve it's the same body with an orifice installed, to reduce the port size.

News to me the the Cv across the valve changes because the pipe size connected to it does? If nothing inside the valve changes?

I know if you add tailpieces to make a transition, you have to account for the pressure drop in those pieces.

Maybe the Cv number is a calculation not from and actual flow test. There is a defined test and venturi tube used to flow test valves and get actual Cv numbers.

Certainly if you add pipe and fittings you calculate EL "equivalent length" to get the pressure drop in the entire piping circuit, that shouldn't change the valve Cv?

I'll check with the lab folks that flow test our valves tomorrow.

Solid_Fuel_Man

I want to talk to some lab folks too! Kid in a candy store hotrod

GroundUp

I'm looking forward to hearing the outcome!

hot_rod

Possibly in an effort to use one body for both sizes, the reduced port style passage creates a flow restriction with a compromised flow passage, that could account for the difference. Maybe that is Joe's point?

In my mind it's not really a pipe size induced condition, sounds like a flow restriction at the ball in the body.

If so adapting 1" tube to the 3/4 body gets the same result, a lower Cv?

Think of a variable orifice balance valve. You read the pressure drop across the orifice, on the PT ports. As you turn the knob you actually change the size of the orifice and the Cv changes.