In the two hospitals I have recently worked in, everyone is extremely respectful of 'pumping breaks'. The nursing mom simply mentions to a co-worker or two that she has to run and pump, and they cover for her. They generally pumped about 3 times a 12-hour shift, as I remember. I know of at least one mom that pumped more often, and nobody had a problem with it. If you believe it will be a problem, I'd talk to your manager and see what can be worked out.
I do have a funny story though.
One of the Residents I used to work with was a nursing mom, and she was in the pumping lounge when a code went off. She showed up with breast milk splashed down her scrub top, calmly put on an isolation gown to cover it up (and because it was a body fluid...lol), and started giving orders. Later she said that she was expressing milk so well, that when the code went off, she couldn't get the milk to stop flowing and she actually showed up with a couple of washcloths in her bra. The nursing pads were not doing it. I wish I had that kind of supply when I was nursing!
We all had a good laugh and teased her for 'stuffing' later :