where did you fail, timed section or boss fight?
If you failed in the timed section, 8 minutes is extreme overkill when you do it methodically. Only turn one valve at a time to prevent squad members from getting stuck in the spawn and stay on the middle raised platform with the main valve, all of you. That platform gives a GREAT overlook to all three spawn areas, allowing mass stunning as soon as the enemies exit their doors, and only has two ways enemies usually come for you. Stun mod sticky bombs, airburst seekers, incendiary ammo, shock/incendiary grenades, anything that has enough radius to stun the majority while you all burn out the runners. Have one player moving twords the next valve as the last enemy from each wave is being wiped, and no one else leaves the platform.
If you failed at the boss room:
The first two waves should be easy enough to deal with. It's the third and the 4th that are the rough patches for most.
Before the start of the third wave, when one enemy is left in the room, check your ammo and run out for a restock if it's even nearing half capacity. Also, use this time to collect medkits dropped by the first two waves if need be. At the start of the third wave, have two squad members on each side of the room, on the side you entered from. Three runners/shotgunners come up each side, with 1-2 on each sometimes funneling into the center aisle. Stuns in any form are very helpful here as well. Burn from distance if you can, and with blind fire if you can't.
Before the start of the 4th wave, same thing applies...leave one alive, restock and collect medkits if need be. The main boss and his guards enter from the opposite side you entered the room from, descending the staircase. The bottom of the staircase is a great point to methodically launch stuns against them all at once, and someone in group running a LARGE (185-200) mag LMG with incendiary ammo helps a ton as well. When you're out of stuns, draw all of them to the side of the room you entered from, then have your highest dps run around the edge of the room to the staircase they came down from, and to the top of it. They don't like to climb back up the stairs, and your highest dps should have no trouble turning their attention around to protect the group. Use the control room as a safe spot, as there is no cover to be had up there, launching whatever you can at them. Bouncing threat levels back and forth should have the Guards spinning around at the base of the stairs, always with their weak points facing someone that can cook off their ammo. Once the Guards are down, take out the main boss..he's squishier, but he packs a punch.
