1st assuming its a ShurFlo,
My guess is with little info is
the diaphram heated up while running empty and the synthetic rubber broke down into bits and now that the system is primed and trying to pump water again so your getting the bits of its current rubber demise in the water now...A rebuild kit is the solution to the problem if you disassemble the pump and its found to be true...The pump uses a staged compression cycle through the diaphrams in the pump and with a rupture in one of the three chambers it will continue to move water but will not achieve the pressure required to trigger the off cycle switch which is also a diaphram connected to a piston switch.
There are variations throughout the evolution of these reliable 12v system pumps, the number on the side of the pump is required for the correct kit to be looked up, its in big print and the 800 number on the side of the unit at the bottom can be called and your good to go in a few days. ShurFlo also can point you to a local part supplier in most cases.
If its rubber...I have seen black alge
form in used little systems...check for this too.
I'm trying to figure out a water system mystery. I'm just back from a 4000+ mile trip, during which I did not use the water system, but rather containers for water and toilet flushing. During a rest break on the return trip I noticed that the water pump switch had been inadvertently turned on. The pump sounded very subdued, however, and not its usual busy noise. I have no idea how long it had been on, but I don't think for very long. There was no water in the tank.
When I got home I put some water in the tank and turned the pump on. Again, not its normal noisy self. Out of the faucets came some blackish particles, some in the form of flakes almost like fish scales but definitely black. My system has an accumulator and I thought it strange that the pump would never shut off, as it usually did once pressure was up and the accumulator was charged. Just ran and ran, and did not produce the usual flow of water— more like about a third of its usual volume and not in a steady flow.
So. I haven't done anything yet and was wondering what folks here might think is going on. I won't have time to work on it for a few days so there is time to accumulate ideas. Anybody got any?