Ask SHC #6: Balance Stage II EVR (Enhanced Vapor Recovery) and Purpose of Venturi Devices In Coax Hoses
Posted: | Author: Matt Schuessler
The Balance system which has been the preferred choice of stage II vapor recovery for many fuel marketers in California, has received serveral improvements over the years. One of particular interest is VST's venturi which has turned a physics phenomenon into an everyday device that deserves more attention. What is a venturi? The purpose of a venturi (liquid removal device) is all about keeping the Stage II vapor return path open and working properly inside a coaxial Balance hose. But In order to understand what the venturi does, a basic understanding of how Balance Stage II vapor recovery works is needed. Read on…
Balance Stage II – What is it? How does it work?
- First off, if you’re unfamiliar with Stage II then study this PDF called “How Balance Stage II Vapor Recovery Works.”
- Next, watch how a venturi works (2 min video). This is how a Balance Stage II vapor recovery coaxial gasoline hose manages to extract fuel that is ‘topped off’ into its outer/vapor hose: https://www.youtube.com/watch?v=hLZkPFrQCDk
- Then, watch this VST training (1 min video), cued up to the point where they demonstrate proper positioning of the venturi pickup tube within the coax hose. https://youtu.be/2pCQEw7FDqc?t=154
Coax Stage II Vapor Recovery Hose Operation
Fuel arrives from the storage tank (aboveground, or below ground; AST or UST) through the connected piping, flex connectors, and shear valves, then up/into the dispenser, through its filters, electric solenoid/blending control valves, meters, and eventually out the hose outlet, through the “hanging hardware” (whip hose, breakaway, curb hose, and nozzle), into the car’s filler neck, into its tank.
Coax Stage II Balance Vapor Recovery Hose Construction
A Stage II Balance EVR vapor recovery gasoline hose is a coaxial device; a hose inside another hose.
- The outer “vacuum-cleaner-looking” hose with coiled internal reinforcing wire is the vapor return path.
- When filling older cars, pre-2004; e.g. non-ORVR Onboard Refueling Vapor Recovery, the vapors displaced inside the vehicle’s fuel tank are pushed out of the filler neck, so the outer hose is there to provide a closed return path back to the storage tank.
- Newer cars, post-2004, are ORVR equipped. They have a carbon filter canister in their filler necks which traps gasoline vapors and prevents them being exhausted back out into the hose, or atmosphere. So, these arguably don’t require Stage II systems, at all, since they don’t allow vapors to escape the car’s fuel tank. And this is why “one day” here in California, Stage II Vapor Recovery will indeed go away for good. That moment in time is referred to by the EPA as a “Declaration of Widespread Use,” and will take place once California Air Resources Board (CARB) calculates that enough Californians own and drive newer ORVR-equipped cars that we can yank the plug on Stage II.
- The inner product/fuel hose is a smaller hardwall hose, filled with liquid gasoline under pressure coming from the submersible turbine pump (STP) in the storage tank.
Topping Off Creates Problems
Now, I never understood why folks insist on topping off in the first place. I mean, how do you pour eight ounces of water into a 6 ounce glass? But, somehow the public are convinced they’re ‘squeezing’ those extra quarters and dimes into their tanks. Instead, they’re pushing the excess fuel back out of the car and forcing it into the hose, through the rubber nozzle ‘boot’ that is sealed against the filler neck opening. This is why when you top off, you end up with fuel dribble down the side of the car, and this is why you need a venturi inside the hose to clear the obstruction.
Venturi Clears Liquid Obstructions
Perhaps you can now see that were it not for the presence of a venturi device residing in the “low point” where the hose naturally drapes/bends between the car and the dispenser, any excess fuel topped off by the public would settle in that lowest point, create a physical obstruction (blockage) in the outer hose, and defeat the Balance coax from providing that needed vapor return path back to the tank. INSIGHT: When customers complain of nozzles chronically clicking off, that can often be a sign of a failed venturi, so accumulated fuel from prior customer(s) topping off sits trapped in the outer hose, unable to be cleared by the inoperable venturi.
Vac-Assist (Healy) Comparison
Healy EVR systems work using a (VP1000) vacuum pump inside each dispenser. They too have coax hoses, but they’re inverted as compared to Balance. With Healy, fuel under pressure flows out the outer hardwall hose, and vapors get pumped back from the nozzle via a very small inner tube. Therefore, there is no venturi device since the vacuum pump runs continuously during any fueling period, from the moment the dispenser is authorized, to the moment the customer hangs up the nozzle.