Just bought an older prochem legend se. Been working fine but the last three jobs It starts to drop pressure after about about 15 20 seconds after pulling trigger on wand. I back to do dry strokes pull trigger again it starts out fine but once again after pulling trigger 15 seconds or so pressure drops about 30 percent. It like if I give It a few seconds pull trigger it's normal then pressure drops within a few seconds. Could it be bladder tank?