, , ,

Morrison Bros FMMASO Overfill Prevention Valve


The ASO series of valves is used to shut-off the air supply to an AOD (Air-Operated Diaphragm) pump when the liquid level approaches full capacity.

The ATO valve is used to turn on the air supply to an AOD pump when the liquid level approaches the full capacity.


Standard Features
  • Installs directly into a 2″ female threaded tank top opening
  • Accepts ¼″ air lines
  • When the ASO valve closes, the air supply is diverted to an audible whistle on the 91S and 91EXS models
  • Operating temperature range is -10°F to 185°F
  • Air flow capacity is 20 CFM @ 100 PSI. Maximum air pressure is 100 PSI
  • Valve automatically resets as liquid is removed and the air pressure to the valve is turned off
  • FMMASO-91 and 91S shut-off height is 6½″ from the tank top
  • FMMASO-91EX and 91EXS shut-off height is 17⅜″ from the tank top
Construction Details
  • Valve body and collar: Anodized aluminum
  • Float: Polypropylene
  • Float rod and valve spool: Brass
  • O-ring seals: FKM
  • Hardware: Stainless and plated steel
Code Compliance
  • ULC Listed
  • Florida DEP EQ 576
Patent 5007450
  • Valve with optional alarm for use on used oil evacuation systems which use an air operated pump
Weight 5 lbs
Dimensions 24 × 6 × 6 in
Body Length

Standard, Extended

Audible Alarm

With, Without



Scroll to Top