Crosman 1720T ?

[Gwelo]

Just dusted off my 1720T after a 2+ year hiatus.
Sitting at 1000psi, I filled it to 3000 and, while bleeding the line the gauge continued to drop to 1800 where it stopped. Hmmm, tried again, same thing only stopped at 2200. Tried cocking the pistol and tried it again. This time stayed at 3000 while I bled the line.

Shot it over a chrono and all seemed well. AA 10.3 started at 620 fps up to 650 and then down to 620, 40 shots!

Went to fill and it did the same thing, will not maintain pressure when I bleed the line, even when cocked. Stopped at 1600, tried several times, cocked or not. Stops at random pressures.

Any ideas? Pistol is factory, no mods.

Is there a check valve in the fill port assy?

 

[Struckat]

Yes the fill port has a check valve. Sounds like it’s sticking.

 

[r1lover]

Had the same issue. I bought a EDgun EaZy quick fill trigger so I never have to worry if/how much air I lose when filling during a match. Gun's check valve closes instantly upon releasing the EaZy fill trigger. Line pressure from tank stays up.

 

[rcarlisle]

I've had a little luck putting a small drop of silicon oil on the fill nipple and then attempting to fill the gun. Pressurizing and depressurizing the line several times can help the oil lubricate the check valve. Easy to try and may save you the time of opening up the gun.

 

[Gwelo]

I've had a little luck putting a small drop of silicon oil on the fill nipple and then attempting to fill the gun. Pressurizing and depressurizing the line several times can help the oil lubricate the check valve. Easy to try and may save you the time of opening up the gun.

I did exactly that, drop of silicone oil, fill to 2200, it dropped to 1800, fill to 2200 again, it stayed so fill to 3000 and it held! Time will tell but so far, so good!
Thanks rcarlisle!!

 

[Struckat]

If it continues, it’s an easy fix.

 

[dreamweaver]

I have a 1720, 1701 and prod. All with the same foster fill nipple. I've had to do this a few times. Easy fix. Bleed air from gun and remove the fill fitting by unscrewing from the air tube. It's only 2 pieces. 3 if you count the o-ring. Remove the inner check valve by pushing it out of the body. It slides in and out of the body and it's not threaded as it might seem. Clean the inner portion of the body with a q-tip as well as whiping off the check valve and o-ring. Lube with some silicon oil, reassemble, fill with air and off you go.