I know what back pumps are and I never experienced any back pumps with EPI-V, but if it is "Back Pumps" as Tiny is suggesting, he is 100% right, Taurine is your friend (5-10g/day) depending on severity!
I decipher the difference between back pumps and LBP (low back pain) as back pumps only happen while in the gym and may last for like an hour or so after, but minus that are not a constant thing. While LBP is constant, oh it may be worse while lifting (aggravated), but will always have at least a slight presence!
Ya know, I'm not 100% sure where Morry (fellow member of the forum) got it from, but when I was experiencing back pumps it just so happened he was too and we split either a kilo or 2 kilo's of pure taurine powder, some bulk place he knew about and it was only like $20-30 a piece, so it is definitely cheap enough to buy and just have on hand, because there are tons of hormones and prohormones out there that will cause back pumps, so it is worth a try to see if it helps!
Good call Tiny!
The Doc. has spoken!