Pump running, not pumping

I have an older pump, newer well. The pump is a Sears model (Sta-Rite) and is above ground. The well is 180 ft. I have a gauge in the discharge side of the pump and this gauge reads Zer0. The Pump runs but sounds like it's not working very hard. My question is, How do I prime this pump as this is what Iv'e been told my problem is. There are two black lines coming up through a steel casing, then going into the pump. And how much water is usually needed for a prime?

 

The amount of water is anybodys guess. If the footvalve is working, 5 gallons or less should do it. If not, you may never fill it up.

bob...