Drafting Tip #09 - Horizontal v. Vertical
 
By President Mark Davis
January 1, 2015
 

We have discussed the importance of apparatus positioning before when it comes to drafting. While digging through some older photos last week we found a couple of photos of pumpers drafting that we thought we would share. It is important to remember that unless you specify anything different, your pumper is going to come from the manufacturer with two (2) 10-ft lengths of suction hose sized to fit your pump's primary suction inlets.

We are an advocate of rural pumpers carrying more than 20 feet of suction for the purposes of, 1) reaching water sources that are farther than 20 feet away from where the pumper can park; and 2) drafting using dual suctions so that maximum pump performance can be achieved.

Keep in mind however that "lift" is perhaps the greatest challenge for a centrifugal fire pump: there is little we can do to compensate for that lift short of placing the pump as close to the water's surface as possible. This of course is where apparatus positioning comes in. There will be those times when an operator cannot compensate for lift. That is fine - just understand that as lift increases - pump performance decreases. One example that often is used to note reduced performance due to lift is: A 1,000 gpm pump drafting through 5" suction hose at 10-feet can only pump 590 gpm at 20-feet! While these values may not be exact - they are very representative of the effects of vertical distance on a fire pump.

The good news is that horizontal runs of suction hose are not as problematic to pump capacity. While suction hose does have friction loss associated with it, much longer horizontal runs can achieve higher flows than had that same run been vertical. Again - a good reason to carry more than 20-ft of suction hose.
 
Hereford's Tanker Support 444 (1,000 gpm) drafts without any problem through 30-ft of 6-inch suction hose at this tanker fill site.
Hereford's Tanker Support 444 (1,000 gpm) drafts without any problem through 30-ft of 6-inch suction hose at this tanker fill site.
Winfield's Engine 142 (1,500 gpm) drafts through 100-feet (yes, 100) of 6-inch suction hose during the testing of its automatic air primer. The pumper was able to achieve a flow of 1,000 gpm at a lift of just over 5 feet.
Winfield's Engine 142 (1,500 gpm) drafts through 100-feet (yes, 100) of 6-inch suction hose during the testing of its automatic air primer. The pumper was able to achieve a flow of 1,000 gpm at a lift of just over 5 feet.
 
The Winfield test used a floating strainer.
The Winfield test used a floating strainer.
The dry fire hydrant had an air leak, thus it was not used during the Winfield test - the floating strainer was used instead.
The dry fire hydrant had an air leak, thus it was not used during the Winfield test - the floating strainer was used instead.
 
Clinton's 2,000 gpm pumper drafts from quite a lift at this water supply drill in Pleasant Valley, MD. Lifts such as this one "kill" small pumpers - and of course, they still reduce the capacity of larger pumpers.
Clinton's 2,000 gpm pumper drafts from quite a lift at this water supply drill in Pleasant Valley, MD. Lifts such as this one "kill" small pumpers - and of course, they still reduce the capacity of larger pumpers.