That could be the problem. But it sounds more like a valve going bad. That's more typically the reason for surging like that.
I would recommend first just taking apart that valve. First, turn off water to the entire system. Then, once you get the top off and guts pulled out, turn water pressure back on to flush out the valve. Next turn water pressure back off. Next thoroughly rinse off all the parts you remove and replace them like they were originally. Tighten the valve back on and then try it. That may fix your problem.
If that doesn't fix it, replace the 3/4" pipe you removed.
Finally, if that doesn't work then you may need to replace the entire valve.