zone valve bypassing question

alotlikeearl

Didn't get any response on the radiant wall so thought I would try here.  If someone piped a boiler with the circulator on the supply side pumping toward the expansion tank (bladder type) instead of away from it,  could that cause one of the zone valves to allow water to bypass when the boiler is fired?

              Thanks!   Jerry

billtwocase

shouldn't matter

you have a bad zone valve. What type? Head in manual position? Thermostat problem?

Eric_32

A zone valve...

is basically a motorized shut off, like an electric ball valve. It's either on or off, there's not enough pressure in a heating system to be able to push thru a "good working closed zone valve" no matter where the zone valve or circulator pump is.

There may be some sediment lodged in the valve seat and not allowing it to close fully.

Mark Eatherton

Really?

Then why does Honeywell give a "Maximum close off rating" capability of 8 PSI for their high Cv valve? 8 PSI = 18' of head...



I have seen whole apartment complexes where the V8043 series zone valves were bypassing because their pumps were so over sized. You could tell because when it got cold enough to start the pump, the residents opened their windows...



We put a VFD on the 5 HP pump and suddenly, all the windows closed.... and the energy consumption of the property dropped 40%.



Valves can be caused to bypass. But more than likely, there is an obstruction (solder drip or other) holding the ball open. I've also seen the black rubber balls shrivel/wrinkle and cause bypass.



Here is a link to Honeywells valve data http://www.forwardthinking.honeywell.com/related_links/water/5000_series/install/95c_10932.pdf



ME

billtwocase

i agree Mark, but

he never said he had a Honeywell zone valve, and I am assuming he doesn't have an over sized pump, or have a 60 room apartment building. I could see a constant circulation system possibly doing this, but if the end switch is operating the circ, shouldn't be an issue other than it is not closing due to a bound up actuator motor, defective ball, etc

Mark Eatherton

Understood...

I was responding to Eric's response. Not chastising, just educating.



ME

billtwocase

I knew where you were coming from

and it's all good Mark. Nothing stated by you was like shooting from the hip. It is also possible  like anything else, and thanks for your valued input, not just to this thread.

Eric_32

ok,

Ok I stand corrected. What does that rating mean in layman's terms?..  I'm guessing differential pressure between the inlet and outlet of the valve?

What is a VFD? Is that the same as a differential bypass valve?

Brad White

PSID

When mentioning pressures in whatever units (Imperial units in this case, psi), we add "a" (psia") for "absolute pressure" referenced from a perfect vacuum, "g" for "gauge", meaning as distinct from absolute.



Then we use "d" ("psid") for "differential" and you are correct, it is the differential across an object, be it a valve, fitting, pump or system, at a given time.



Basically the term "psi" will suffice and it tends to mean "gauge", what you are seeing at any given moment in the field. We use the suffixes to be more specific to an application.



A last note on that is the "Cv" factor, the flow rate across an object, (usually valves), at a pressure differential of 1.0 psid. So that is one specific application of the term.



Finally, to your question...:)



The "Maximum Close-Off Rating" is the maximum pressure (differential), against which a valve will remain closed. An ounce more and the valve will begin to open. It is a design balance between springs and an actuator's power to overcome that.



Typically but not always, the close-off rating is applied to spring/plunger type valves where the motive force is on the bottom of the valve seat, pushing upward in direction of flow.



As an example, say you have a control valve with a maximum close-off rating of 25 psid. You may have 40 psig on the inlet side (higher than 25 psid), but have 30 psig on the outlet side (also higher than 25 psid). However, the differential is 10 psig, below your limit so the valve will work in that application.



For that matter, the valve could see inlet pressures equal to the maximum design pressure for the valve body (e.g. 250 psi, 300 psi) and hold perfectly well so long as the downstream pressure is within the close-off range. It is all in the differential.



Rotary type control valves, such as characterized ball valves, have higher close-off ratings, sometimes close to or equal to the valve body rating (e.g. 125 psi, 150 psi). This is because the motive force, the differential, serves to move the ball sideways, but not lift it. Does that make sense?



A "VFD" is an acronym for "Variable Frequency Drive", a speed controller for a motor. May also be called a "Variable Speed Drive" or VSD, but the term "frequency" or Hertz modulation, is specific to how the better ones. Smaller fans for example use variable voltage, so those would be lumped into the more generic "Variable Speed Drive" or VSD.

Big Ed_4

Sometimes

They just go bad ... Depends the make of what goes wrong ..I seen the honeywell rubber ball crack and others stick open...

alotlikeearl

Thanks!

Thanks for the insight guys!!

                       Jerry

hot_rod

also

that close off pressure is different in zone valves, even of the same brand.  Higher Cv valves have larger holes in them   so the close off pressure may be lower than a valve with a smaller shut off orfice and lower Cv.



Things get stuch in zone valves causing un-wanted flow.  Solder balls, copper shavings, debris, etc.  Especially after any work has been done on a system.



Also some brands of ZVs get an imprint in the close off mechanism that can cause some bleed by.



hr

bob_46

Opposite

I've seen White- Rodgers 1311 valves, ( the big three wire ones with the upside down S.S.

cup with a hole in each side) that won't OPEN if the ∆ P is too high.