Air Gap/Anti-Siphon Fills
There are usually two reasons for an air gap fill. This would typically be on direct fills. i.e. not from the truck pump.
The fire department wants to fill and disconnect from the water source without losing water. it the fill is near the bottom of the tank, the water could potentially drain to the fill level.
If they are filling from a municipal potable water source, the water authority would be concerned with contaminated tank water potentially back flowing in the municipal water source if the pressure in the tank is greater than the water source.
For Situation one:
The most common solution is the use of a “J” fill. These are similar to the Morita fills. See drawing 703-5503J.pdf. There is just an internal air gap flush with the underside of the cover. See the image below.
Situation two:
This is much more stringent. The generally accepted practice is that the fill line must be permanently mounted external to the tank to ensure a water leak in the plumbing will not allow contaminated water to siphon out. The gap between the top of the tank (fill brim) and the fill port must be two times the diameter of the fill line. A 3 inch fill would require a six inch air gap above the fill brim. The gap should never be less than one inch. See the illustration below.
UPF would prefer that any external plumbing be provided by the truck OEM. We can provide clamping surfaces for the plumbing.
Examples of UPF tanks with variations of air gap fills would be GPM 770-3290M.pdf and Gradall 770-3690I.pdf. The GPM tank shown below has has internal plumbing which may not be acceptable for situation number two. This would need to be be confirmed with the OEM or end user. This would be a good alternative if acceptable.
GPM Ellip-T 773-0080A.pdf has external plumbing. Doesn’t really meet the requirement above the fill brim.
Gradall 811-0474.DWG is another variation. Tank is plumbed internally from the bottom and the customer bolts an air gap assembly to the tank top. Current customer design is to the right.