Vacuum has got worse but the pump sounds and draws current exactly as before — where do I look?

Look for internal clearance, not for a leak. A failure that changes noise or current is mechanical; a failure that changes only the pressure is almost always a gap somewhere inside the pump that gas can flow backwards through. That distinction narrows the search enormously and most people skip it.

The reason it is silent is worth understanding. Gas leaking from the discharge side back to the suction side inside the machine does no work on anything — no rubbing, no extra torque, no noise. The pump keeps compressing the same gas over and over. Ultimate pressure degrades steadily, everything else looks identical, and troubleshooting goes looking for an external leak that is not there.

Where the clearance is depends on the pump type. On a liquid ring machine it is the port plate face or the cone: the face wears, the axial gap between it and the impeller opens, and vacuum falls with no other symptom. On an oil-sealed rotary vane pump it is vane height and the stator bore. On a dry scroll pump it is the tip seals. On a Roots booster it is the rotor-to-casing gap after a thermal event.

Before you order anything, do the one test that separates the pump from the system: blank the inlet with a solid blank and a known-good seal, and measure the pump's own ultimate pressure on a gauge mounted at the pump. If it meets the manual figure, the pump is fine and the problem is in your chamber, your line or your gauge. If it does not, the pump is the problem and you now know which component to measure.

A service kit will not fix this. Kits restore sealing at the shaft and the static joints — they do not change clearance. Ordering a kit for a clearance problem is the single most common wasted purchase we see: the pump comes back leak-tight and still will not pull down. Measure the wearing face first, then order.

Tell us the pump model, the serial number, the ultimate pressure you measure blanked, and the figure from the manual. We will tell you which face to measure and quote the part that actually restores it — or say when the machine is past the point where a part helps.