Minimum distance between supply and return on a primary-secondar

Mark Eatherton1

but the distance between any tees or elbows upstream and or downstream can be problematic. Siggy wrote an article on that which spells out all considerations, and I tried to retreive it from PM Mags website, vut their search engine is down. Maybe HR will post it.

ME

Brad S

Minimum distance between supply and return on a primary-secondar

I am doing a primary-secondary pumping system. In his book Pumping Away, Dan states that the supply and return, off of the primary, should be no greater than 12 inches and ideally 6 inches apart. I have a limited space and am wondering if I can pipe it even closer (4 inches apart) or if this would cause some other problem?

Thanks,

Brad

kevin coppinger_4

I don't....

see a problem with that. It will hepl to keep the ghost flow down. kpc


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Unknown

Brad

The terms in the past were less than 12" apart. But based on the size of the system and relative pipe sizes this could differ a bit. The newer istructions from folks like Tekmar and others now spell out less than 5 to 6 pipe diameters apart based on the diameter of the primary main. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

www.burnham.com

Kal Row

Basically…

Closely spaced tees require less than 6 pipe diameters between the tees and preferably 12 pipe diameters on either side of the tees – at least have 12 pipe diameters on the upstream side

- 12 pipe diameters is also important preceding flow checks – and is why the Grundfos 15-58fc with the spring check on the outlet is not as quiet as a taco 007 ifc with the check in the inlet eye – outlet turbulence makes the check chatter at higher flow rates - like in a primary loop - i have a pri/sec/injection system with three 15-58fc's and the boiler loop's one is audible whereas the others are silent - and yes, i have swapped them around and cleaned up any dirt on the checks – (dirt really makes them chatter)

– when siggi (hydronicpros.com) says 12 diameters to a check, you comply or “face the music” literally

mabe this info will also help
http://www.tekmarcontrols.com/acrobat/e021.pdf - good section on close-t's

hr

Closer the better

I have T-Drilled them as close as 2" to each other. I have also teed into opposite sides of the primary loop for a pair without any problem.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

hr

From Siggys column

"Look ma no cavitation"

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,4270,00.html

Don’t locate the circulator upstream (pumping toward) the expansion tank. If you do, the differential pressure created by the circulator is subtracted from the static water pressure at the pump inlet. Reach the magic number and you’ve got cavitation.

Don’t put throttling valves, flow checks or other components with high flow resistance near the circulator’s inlet. Anything that creates a significant pressure drop coaxes the water closer to cavitation at the worst possible spot.

As a general rule install at least 10 pipe diameters of straight pipe upstream of inline circulators. Use only isolation flanges or full-port ball valves for isolation.

Don’t operate the system at low water pressure. The lower static pressure at the circulator inlet, the smaller the pressure drop required to bring on cavitation. Closing the make-up water valve will eventually cause the pressure to drop in any hydronic system. Maintaining a decent static pressure is especially important in low-rise buildings that don’t have the piping height to inherently generate the pressure.

Don’t design for high water temperature operation. The higher the water temperature, the higher the system pressure must be to prevent boiling. Sometimes you may even come across a circulator that operates quietly at low water temperatures only to fizzle and pop when the system gets up to higher temperature. Do be especially careful in designing systems with high head circulators, or multiple circulators in series. The higher the pressure differential across the circulator(s), the more the pressure at the circulator’s inlet will drop if, for example, the circulator pumps toward the expansion tank, or the static pressure gets too low. Do install a good air separator to quickly purge the system of dissolved gases that can create “gaseous” as opposed to vapor cavitation. Although not as destructive as the latter, gases going in and out of solution as they pass through the circulator will still get your ear’s attention. Figure 2 shows a system that no enlightened Wet Head would ever install. Look it over and describe eight things that are wrong. (Look for the answers at the end of the column.) Decavitating: No, this doesn’t refer to some new dental procedure. It’s about what to do if you’re called in to fix a “noisy pump” complaint. After ruling out mechanical problems like motor bearings, or couplings, cavitation is almost surely the problem. Check the static pressure and water temperature near the circulator inlet.

Remember that low pressures and high temperatures encourage cavitation. Also look for piping components that could cause a significant pressure drop just upstream of the circulator. Always check the location of the expansion tank relative to the circulator. One or more of these things is almost always responsible for creating the problem. Circulators pumping toward expansion tanks are common in older systems, as are high water temperatures. If, for example, the original circulator was replaced with a higher head model, or the original one-zone system was subsequently divided up with zone valves, there could well be a higher ³P across the circulator. Perhaps just enough higher to cross over the cavitation threshold under certain conditions. It’s also wise to check any strainers near the circulator inlet. Once you’ve confirmed cavitation, isolate the circulator, remove the impeller and inspect for damage. Look for abrasion of the impeller and volute. If anything but extremely minor abrasion is present, the affected parts should probably be replaced. Two adjustments that can sometimes correct mild cavitation are boosting the system’s static pressure and/or lowering the system’s operating water temperature. Obviously you have to be judicious in adjusting water pressure upward to avoid creating a new problem with the relief valve. Likewise, lowering the water temperature too much might correct cavitation but spawn the new complaint of insufficient heat delivery. Remember, it’s a system; changing anything can affect everything. If you’ve tried adjustments to static pressure and water temperature to no avail, and you’re convinced the circulator model is appropriate for the flow/head requirements of the circuit, it’s probably time for surgery. If valves, elbows or other head-robbing/turbulence-inducing components are located near the circulator’s inlet, they’ll probably have to be removed, or at least relocated. While you’re at it, be sure to relocate any expansion tank that’s installed downstream of the circulator. Next month we’ll look at ways of predicting the occurrence of cavitation on paper, rather than waiting to see if the circulator runs as smoothly as you hope it will. In the meantime, keep up the pressure to eliminate cavitation — literally.

Answers to Figure 2: Flow-check and tight turns near circulator inlet creates significant pressure drop and turbulence. Pumping toward expansion tank lowers circulator inlet pressure. When only one zone is open circulator operates at high pressure differential. High water temperature and low pressure reduce safety margin against cavitation. Use adifferential bypass valve. No air separator is used. Misapplied high head circulator. Use circulators with “flat” pump curves for zone valve systems. Low-rise distribution system cannot inherently maintain system pressure. Closed make-up water valve will allow system water pressure to drop over time.



John Siegenthaler, P.E. - John Siegenthaler, P.E., is principal of Appropriate Designs, a consulting engineering firm in Holland Patent, N.Y.

I'm not sure how the Taco operates with the check on the inlet. Makes me wonder at low fill pressure if you aren't dangerously close to the cavitation point??

Also some good reasons to leave the fill valves OPEN

hot rod


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"