Normally Closed ?

Unknown

As far as I am aware, all Honeywell control descriptions are based on a "No Power" state. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.

jim post

What is normal?

Well now I did it. Upon further review and enlightenment from The Wall, it looks like I have my no power overheat zone valve exactly backwards...
If a valve is "normally" closed I assumed that meant under normal operating conditions...when it has power....BUT from further review of the literature and diagrams...I think they are saying under "normal" conditions the power is off. Before I tear into this to correct it...I just want to be sure.

So is "Normal" power on or power off?

Any tips on how to unsweat, spin and resweat a zone valve would also be appreciated. :-)

jp

Ron Schroeder_3

in North America

we assume that it is normal to have an endless supply of power on. It is our constitutional right.

Given the assumption that we are entitled to uninterrupted power, it would be more correct to specify a control valve that closes under power and has a spring wound motor to open it should the electricity drop out.

As an aside, please make sure that the port that opens is as large as possible for the given pipe size.

Joe Mattiello

Taco Zonevalves


You will have to un-sweat the valve index it 180 degrees and re-sweat it. The actuator can remain in the existing orientation. As for normally closed, that would be the valve position, and not the electrical contacts which are normally open. When the thermostat closes on temperature fall, it completes the circuit allowing 24 volts to flow to the valve. When the thermostat is satisfied it opens and cuts the 24 volts to the valve. Hopefully this answers your question.

Taco, Inc.
Joe Mattiello
Technical Service Technician
joemat@taco-hvac.com
401-942-8000 X 484
www.taco-hvac.com

Mike T., Swampeast MO

The "normal" state is the rest state, e.g. unpowered.

A normally closed valve is closed until power is applied. When power is removed it returns to the closed or "normal" state. Most zone valves are, I believe, normally closed.

Normally open devices (those that close when power is applied) are generally used when the open state is required to prevent damage and/or danger. Flue dampers are a very good example of a normally open device. In the event of control failure, they will remain open thus keeping flue gasses from spilling into the structure.

Joe Brix

Honeywells

are available in both open and closed models. True, most are normally closed. I would think it's easier to energize the value open only on a call for heat from the thermostat. That's why a manual open lever is provided. Makes purging zones alot easier when everything is normally closed and you can manually open each zone one at a time.

rb_6

N.C. /N.O. and port size



Normally closed requires power to open.

Normally open requires power to close.

...as far as port size...let’s talk marriage counseling for control technicians.

One of the major reasons for customer dissatisfaction with water based HVAC systems is the wrong control valve characteristic with the wrong port size (Cv) in charge of maintaining controllability over the system.

A valve manufacturer might offer as many as 5 different Cv's (ports) for say a 3/4" connection for a very good reason…and it gets better...valves come with different plugs which are characterized based on their flow at a % of opening at a given differential pressure. Again for a very good reason.

Controlling hydronics is all about controlling the hydraulics...when we can control the pressure we can control the flow. When we have authority over the flow we have authority over the system. A valve, which is on/off or has a port too big, creates the same control effect as using a hand operated gate valve.

Like all equipment in a system the selection process is an engineered process…we have to do the math. In the case of control valves you have to start with the device you are trying to control. Is it radiant? Is it baseboard? Is it a fan/coil? We also look at the application…is it controlling the fluid temperature or is it controlling the room temperature? Is the valve controlling a pool, spa, snow melt?

Fast responding heat terminal units like fan/coils and baseboard or low mass radiant such as panel heaters have what I call MANIAC characteristics…a little flow and wham…lots of heat. The last thing these types of devices should have on them is a MANIAC valve defined as fast opening, large port (big Cv) on/off action. In fact, at roughly 15% valve opening the MANIAC baseboard or fan/coil will be delivery close to 65% of its rated output at a 20 deg F delta T. What they need is a control/actuator/valve with MELLOW characteristics with 15% of its flow at 65% of its opening to create a 50% flow / 50% output. When you marry the mellow fellow (modulating actuator with equal percentage valve characteristics) with the maniac mistress, you get balance - believe it or not. It’s kind of like partners in business…two accountants makes for a well documented and financially controlled operation but no one does the selling or engineering so it goes broke. Two engineers in a business and lots of design happens but no one does the billing so it also goes broke. You need the technician and the manager to make it successful.

When the MELLOW FELLOW is used, the port size or Cv is selected so it represents between 30% and 50% of the head loss through the circuit it is controlling. If it takes 6 psi to move the fluid through the circuit then the control valve Cv is selected so it represents 2 to 3 psi. If it’s a high mass MELLOW system like a swimimmng pool or a radiant heated concrete floor then the MANIAC valve works fine.

But that’s not what happens…what happens is the lowest cost - biggest valve with on/off action - the maniac valve -gets installed with another maniac – baseboard/fan/coil etc.. and then real people end up owning a psyche ward of systems…complaining about how crazy it is - over and under heating – noisy – gurgling…the never ending complaints which could have been addressed by just simply picking the right valve with the right Cv having the right characteristic for the system...but thats not what happens...which is one of the reasons why people don't trust heating contractors.

Normally open or normally closed …. great question and part of a much much bigger topic.

jim post

Diagrams clear as mud

I piped it like the diagram 6f thinking that this was the power on condition. Yeah, I know it says power off in big print right there. :-)

I am now thinking that it should be piped like 6e. In 6e, the B-port will be the path when I have power and A-port will be closed. Upon power loss(the normal state), B-port will close and A-port will allow gravity flow to my overheat loop...hopefully! Does that seem right?
Thanks,
jp

Mr.Bill

NO, NC? It's how it comes out of the box which in turn is the non powered position

bob young

correction

if valve must be reversed cut back piping on both inlet & outlet and reconnect with two couplings otherwise your valve could very well wind up in the garbage pail. unsweating valves & fittings and re-installing is not a great idea if you have a choice.

[Deleted User]

Said...

like only the Bean could say it. Thank you sir for an excellent, easy to understand explanation.

ME

rb_6

Mark!!!

You're alive! ...and well - I trust!

Have been shining up a fishing lure for your writing talents...snap...click...whishhhhh....plop...tap...tap...hmmm - will he bite...tap....tap...

(ok - snap on the lure...click back the cage...toss out the line...whishhhhh....into the lake goes said writing lure...tap...tap...tap the toes...)

Will call.

Now where did Yates put the bug spray...

Dale

philosophical question

What is normal. I agree that "normal" in the heating world is usually meant in the unpowered position, out of the box and laying on the bench. I still blow into valves and solonoids to see if they are open before I really believe the box. The one place this doesn't hold is with blower door switches. Many schematics show the blower door switch on furnaces as closed in the unpowered position and it is if the door is on correctly. If you test a door switch on the bench it will be open. The twist is that the manufacturer wants the door on when the furnace is off and the door on when it runs. So, what's "normal" for a normally open door switch is to be closed by the sheet metal blower door and allow power from the junction box to go to the furnace.