Kitchen sink faucet seems to drop to near trickle when the water is turned on full (Cold side ... Hot side has always run very slowly). This is not a new installation and there has not been any other plumbing work done in a long time. If I turn on water about half force it will stay on okay but any harder and the clunk sound happens and the pressure goes to nearly nothing. Just seemed to start out of the blue a few days ago and only out of the kitchen faucet. To me seems like an air lock someplace but how to get rid of it and how did it happen to start with? Thanks much for any reply. DaveB
It sounds like an old system with washers, where a washer has come loose, or possibly some object, e.g. a corroded-off screw head, is being pushed into the outlet pipe when the tap is turned on fast enough to move it.
If you shut the supply below the sink and take the valve apart, the issue should be obvious unless it's an object that drops out of sight down the pipe. In that case, carefully turn the shut-off valve on a bit, after first covering the valve opening with a plastic bowl to redirect most of the water back into the sink. Hopefully, this will eject any blockage. You might need a helper to hold that bowl.