direct injection .vs. valve mixing

hot_rod

what type of control is driving the VS? Maybe move the sensor downstream a bit more. Do you have checks on either side of the injection loop? I've had limited luck with thermal traps. They look and sound good on paper, but spring checks are the ultimate "gravity gate"

hot rod

st heat

direct injection .vs. valve mixing

Been experimenting comparing the control ability of secondary water temperature using var. spd. direct inj. on low load radiant systems (40 k btu) using pri. sec.piping close tees and found poor secondary water temp. control from ghost flow. i added 4- 5' deep thermal traps 12" to my injection piping for resistance and found similar results.the secondary water temps. were prett close as per reset in cold weather with big load but in mild weather (partial load)the sec. temps were way too hot. pretty interesting. can any one add experiences. thank you st.

st heat

inj.

no checks at all on the injection lines. the control is a tek 353 (older model ) but good.the thermister was in a good location . i believe i had good turbulant flow . i think the ghost was just to much in mild weather.the orig design was design water temp @105 f 10 zone radiant ceilings using pex and al plates and low expansion was critical. thank you

st heat

spring checks

Mr rod have you had any customer inquiries regarding the tapping sound from the spring checks. st.

hot_rod

No not really

they need to be the type with low "pop" pressure. Most manufacturers will list that spec, 1/2 psi seems to ring a bell.

Also the type with a soft seal, not brass to brass. Look at the check that are being used in many circulators these days, also the same ones used in the B&G Check-trol-valves. There are a plastic, light spring, and cone shaped with an o-ring seat.

Here is a picture of the one Grundfos supplies in the Super Brute series. Inline sweat checks are available from Conbraco and Watts. Those are brass with an o-ring seal so you can solder against them.

Check valves need to be sized to the flow rate not the pipe size, that is a common cause of "chatter" Usually one size smaller than the pipe is right, even though it looks funny it is the correct way to size for noise free operation. Use the manufacturers spec sheets to get the right size for the job at hand.

hot rod

st heat

spring checks

thank you hot rod.