Replies to This Discussion

Permalink Reply by Don Catenacci on April 19, 2016 at 4:51pm

The length of the hoseline is dependent on the hose size, 150 for 1 1/2 inch, 200 for 1 3/4 inch.  Reality though is you can use 2 1/2 or 3 inch hose as long as need be as long as you can hit 200 psi to the eductor at the end of the larger line.  Place the eductor on the end of the 2 1/2 or 3 inch line attach your 150 feet of 1 1/2 inch or 200 feet on 1 3/4 inch and work from there.

• ▶ Reply

Permalink Reply by Mike DiStefano on May 25, 2016 at 10:00pm

Don is right, the size of the hose determines the length after the eductor. The reason for the limitation is due to pressure. There is a substantial amount of pressure loss through the educator(approx. 1/3 of whatever pressure you put into it). A pretty well used pressure is 200 psi at the pump to allow for your hose line FL, Nozzle pressure and FL at the eductor. The foam solution is the same no matter the length. Also remember the GPM of the nozzle must match the GPM of the eductor.

• ▶ Reply

Permalink Reply by William N. Hoehn on May 31, 2016 at 1:55pm

Greg:  This explanation might seem a little long winded, but read through it, even a couple of times to grasp the physics involved.  Energy in a hose line or hydraulic system can be defined by the multiplier of the flow (velocity) times the pressure.  If we examine the action at a nozzle, the pressure at the base is used to accelerate the water until at the exit of the nozzle all energy has been changed to velocity (speed).  In fact the same thing occurs in the throat of an old conventional carburetor.  As the velocity of the air increases, the pressure in the throat decreases, until the gasoline is forced into the air stream by atmospheric pressure from the tank or float reservoir.  This is the same way that the "Eductor" works on the foam line.  The air pressure pushing on the foam concentrate in the bucket or tank, pushes the concentrate into the eductor.  The rate is determined by the 14.7 psi atmospheric pressure forcing the concentrate up the "pick-up tube" and into the metering portion of the eductor. Since the velocity of the water going through the eductor throat controls the vacuum, it is critical to hit this exact flow rate.  If you listen to the eductor, it will tell you when it is operating correctly.  You will hear the tell-tale sounds of cavitation, as the internal pressure on the exit side of the eductor reaches or drops below the vapor pressure of the water. (snapping and popping are normal here, but NOT in a pump)  The viscosity (thickness) of the foam concentrate requires a certain pressure gradient to bring the correct amount of concentrate from the bucket, up the dip-tube and through the metering orifice into the throat of the eductor.  Having the wrong size hose, wrong length of hose, or wrong nozzle size will increase back pressure in the line.  Most of the eductors that I am familiar with require a pressure drop of 70 psi across the eductor when operating.  This means that if you are running a fog nozzle (100 psi) along with the eductor (70 psi) you will only have 30 psi available for hose friction loss.  Putting too small a hose or too long a hose after the eductor will not provide the 70 psi drop, so the water will not reach the critical velocity needed to cause cavitation (zero psi - almost) and thus will not bring the correct amount of concentrate into the eductor for mixing with the water.  You may be wishing to challenge my "zero psi" statement for pressure in the eductor.  Remember the beginning of this reply where energy is the product of velocity and pressure ?  Since the high velocity water in the eductor throat slows down as it enters the exit hose, the pressure rises to maintain the energy equation.  This is where the 130 psi comes from to push the mixture through the hose and out the nozzle.  You might have another, less understood problem, if you have been practicing with AR-AFFF concentrate.  This material has a tendency to gel when allowed to sit on a shelf in the buckets.  Try shaking the buckets rather violently before opening.  This should lower the viscosity (thickness) of the concentrate.  You can use a 5 gallon bucket of water in place of wasting concentrate to check the operation of your eductor.  Fill a 5 gallon bucket with plain water.  Leave the dip tube out until you are ready to start the test.  Adjust pump pressure to provide 200 psi inlet at the eductor.  You will need to do some simple calculations to determine the rate of pick-up.  Example a 95 gpm eductor set at 3% should pull just slightly less than 3 gallons per minute, or the entire 5 gallons in about 1 minute and 45 seconds.  If it is between 1 min. 30 sec. and 2 minutes it is operating close to the desired concentration.  Good luck.  Send another message if this doesn't explain things.

• ▶ Reply

Permalink Reply by Don Catenacci on July 24, 2016 at 11:28pm

Actually Mike, it should be 200 psi at eductor.  It doesn't matter whether the eductor is at the pump panel or several hundred feet from the engine on 2 1/2 or 3 inch hose.

 
Mike DiStefano said:

Don is right, the size of the hose determines the length after the eductor. The reason for the limitation is due to pressure. There is a substantial amount of pressure loss through the educator(approx. 1/3 of whatever pressure you put into it). A pretty well used pressure is 200 psi at the pump to allow for your hose line FL, Nozzle pressure and FL at the eductor. The foam solution is the same no matter the length. Also remember the GPM of the nozzle must match the GPM of the eductor.

• ▶ Reply

▶ Reply to Discussion