control valve on wrong side

[remp]

I have just come across a control valve on a duct re-heat coil on the flow side of the coil. I usually put them onto the return side (leaving side). Is this a major problem.??? Will i get away with it??.... Interestingly we have had 2 actuator failures on this very valve, I wonder is it linked???

Regards,

Remp

 

[tys90]

Thinking out loud here...

Is it possible that they crossed the supply and return lines during install? If they installed the valve in what they thought was the return line, not only will it be on the wrong side of the coil, it will also be backwards with regards to the flow direction too. If it's a normally closed valve then the actuator is opening against both the spring close and the water pressure which might be why it's failing. Have you heard any water hammer like noises when the valve shuts?

 

[DRWeig]

My opinion:

Control-wise, it doesn't matter which side the valve is on.

There are still two schools of thought on the position issue. I was taught to put them downstream to help avoid sucking in air into other parts of the system in the event of a coil leak above the valve. Not sure if that's the accepted answer or not...

As for actuator failure, it won't be linked to which side the valve is on, unless (as tys90 says) the valve is mounted backwards, flow-wise (ie, against the arrow on the side of the valve body).

Let's see what some old-timers say. I'm a controls guy.

Good on ya,

Goober Dave

 

[zuccus]

As tys90 said, I would make sure that they didn't cross the supply and return connections to the coil. This could be detrimental to the performance of the coil regardless of the position of the control valve.

A couple of old-timers have always told me that it doesn't matter what side the control valve is on, however, I still prefer to keep it on the downstream side to keep the coil flooded.

 

[BronYrAur]

I doubt that temperature is the cause of actuator failure in a duct reheat system (temps won't be high enough), but having the valve on the supply does expose it to more heat.

I found the following information on the

http://www.flowdesign.com

web site:

At The Terminal

The preferred location for manual or automatic balancing valves is the return side of the coil, as shown in the detail in the Balancing Valve on Coil Return diagram above. The return side is recommended by ASHRAE and is preferred by many engineers because it will:

Minimize air entrapment
Reduce noise problems
Decrease the possibility of ATC valve cavitation

Refer to Appendix D of the “Coil Hook-Up Design Guide” for more details.



I did a Google search for the “Coil Hook-Up Design Guide” mentioned here, but I could not find anything. Does anyone know where to get that guide?

 

[Wareagl487]

It will work on either side - but I was taught to place it on the return leg side as to "....always keep the coil flooded.." Whether there is a valid reason behind this, I haven't a clue.

Andy W.

 

[ChasBean1]

For commissioning (my forte), I try to implement return side installation for three reasons, whether it be chilled or hot water. But this does not mean the installation will not work correctly, and performance-wise you might not see an issue (immediately):

1. If it is a hot system, some manufacturers have temperature limiations on the actuators. If there is a 180°F limit on the actuator (common to some actuators), the return side is preferred as it will operate at a cooler temperature.

2. If it is a cold system, it is always better to have less thermal breaks on the colder side (e.g. 42°F water) than on the warmer return side (e.g., 56°F water). The return side installation reduces sweating on the electronic actuator, which is more prone to failure when wet.

3. During a water's travel through a coil, the piping becomes smaller (e.g., from 3/4" down to 3/8") and there is a torcherous path through the coil. This reduces pressure of the fluid. If it is a hot fluid, more gases might be stripped from solution with the coil throttling on the inlet side. With a control valve on the return side, the water is at a higher pressure through the coil, reducing offgas, thereby lowering dissolved oxygen content. Lower dissolved oxygen extends equipment life.

 

[Waramanga]

i guess a good reason to have the valve on the return side is that if any air gets released in the dP then it wont end up inside the coil itself.
The point above on noise is good, if you get a squeal, the coil isnt acting like such a 'speaker cone' although water does transmit sound much faster than 3m/s water flows at so I dont know if this point is 100% valid.