Coil balance

A home owner from Philadelphia, Pa says:
I have previously ordered window parts from Swisco over the past years.My window sash weighs 18.37 lbs approx. & has a S160-9 coil balance spring with the 15-111 pivot shoe & 15-150S single support installed with it. Because the springs have broke previously can I install a 10 LB. coil spring instead of the 9 LB. S160-9. If so what are the part numbers for that coil balance spring & the corresponding pivot shoe & single support, Thank You.
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Paul from SWISCO responded:
Hello! For a 18.37 lbs. sash, I would stay with the S160-9. Since the true weight of the spring is 9.5 lbs., two should be more than enough to carry your sash weight. You can reuse your 15-111 if it is not broken.
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