Problem with Silca Floor Pump
 

Mt Silca SuperPista has been a great floor pump for the last 5 years, and I've been using the Shraeder chuck head to pump up my motorcycle and even truck tires.
But now it's as if a valve is stuck. The pump does not leak at all and it does still inflate tires, but if I take my hand off the pump handle, the tire pressure causes the handle to pop up. Also the pressure gauge goes briefly up to the (approximately correct) pressure, then the needle immediately drops.
I'm on my third leather gasket, and this happens with both the presta and Schraeder head, so I presume the problem lies in the pump body?
Any ideas?

I believe there is a check valve in the base of the pump where the hose attaches. Sounds like it is dirty or stuck open.

How do you fix that? I have a floor pump with the same symptoms, though not a Silica.

Every pump has a "check valve" that alows air to flow from the pump barrel into the tube but prevents the air in the tube from flowing back into the pump. These valves are either a ball or plunger in a mating seat or a flapper of some sort. If they get dirty or rusty, you get the symptoms you are experiencing. Remove the valve and clean or replace the ball and it should work fine. The Silca .pdf referrs to the check valve as the "non-return valve".

Section E 2.2 "Cleaning and Replacement of the Non-Return Valve" should cover your problem. The PTFE tape referred to is plumber's Teflon pipe joint tape.

Bella! Grazzi paisanos! Can't wait to get home and fix this.

Silca leather gasket
 

most likely.

are you greasing it?

I've kept it greased, and Im still on the Original one 25 years later.

Though MCM the Selle-anatomica maker was making pump cups and shaft packing for decades
before being convinced to get into bike saddles..

In hundreds of sizes, I just need to Measure the old one. but its not broke yet. :innocent:

+1, The check valve isn't working. The most likely cause is rust. Pumping tends to "squeeze" water out of the air, and it accumulates at the bottom of the pump, eventually rusting either the ball, or seat of the check valve.

You need to disassemble the manifold between the base of the pump and the gauge, and clean or replace the ball (if that design) or otherwise service whatever check valve is there. It's usually not difficult and should take about 10 minutes or so.