HYDRANT FLOW TESTING QUESTIONS

Hydrant Flow Testing Questions

Why should I use a Hose Monster® over the hand-held pitot method?

A few reasons:

  • The hand-held pitot requires perfect positioning where the pitot is half the orifice diameter away from discharge and the pitot tube is perpendicular to discharge. This is nearly impossible to hold by hand, which is why you will see a bouncing gauge needle and inaccurate readings.
  • The hand-held pitot method requires you to guess the required coefficient depending on the shape of the hydrant nozzle. This is not always known.
  • The hand-held pitot requires that the water is discharged out into the open. This method is a risk to safety and can also lead to property damage.
  • The Little Hose Monster™ with the Pitotless Nozzle™ or the steel Hose Monster make it easy to take consistent and precise flow-rate measurements that are FM Approved for accuracy.

How much is the friction loss when I use a hose?

A hose causes friction loss, but it doesn’t matter in a fire flow test. A hydrant flow test evaluates the water supply to determine what flow-rate will be available at 20 psi residual. A hydrant flow test requires three measurements: static pressure, residual pressure and test flow-rate. The reading from the gauge cap on the test hydrant gives you static and residual pressures. The Pitotless Nozzle or Hose Monster gives you the test flow-rate. The friction loss created in the hose results in lower test flow and, at the same time, greater residual pressure. This does not affect the predicted flow at 20 psi, as long as you’re getting sufficient drop from static to residual. NFPA 291 recommends a drop of at least 25%, while AWWA M17 requires a minimum drop of 10 psi.

Previously we did hydrant fire flow tests using a hand- held pitot. Why are our discharge flows different?

The test flow-rate will be less, but the residual pressure will also be higher. This will not adversely affect the flow test when calculating water supply. Remember, the test flow-rate by itself doesn’t mean much. You also need to take into account static and residual pressures. The discharge flow-rates are also influenced by whether you’re flowing from the pumper port or the nozzle port of the hydrant, the length of hose and the flow test device.

Can we use the table found in NFPA 291 to determine the flow based on our reading of the gauge from the Hose Monster?

No. The table found in NFPA 291 is not the same as the Hose Monster flow chart. We provide appropriate flow charts with each Hose Monster or Pitotless Nozzle sold. Flow charts are also available on the Literature Rack of www.hosemonster.com. If you are taking hand-held pitot readings directly from a hydrant nozzle or pumper port, use NFPA Table 4.10.1 and apply the correct coefficient(s).

Do I take into account the hydrant coefficient when calculating flow-rate from the Hose Monster?

No. The flow-rate is measured correctly at the Pitotless Nozzle or the Hose Monster and not affected by the flow characteristics of the hydrant nozzle or pumper port.

Why should I use a Remote Reader?

Three good reasons. It enables you to take the pressure readings away from the flowing water, it keeps you dry, and it also encourages workers to remove and safely store the gauge after a flow test.

Is the Hose Monster or Pitotless Nozzle NFPA compliant? NFPA 291 outlines its procedure using a hand-held pitot.

NFPA 291 is a recommended practice but not a requirement. We are not aware of a standard that requires a hand-held pitot. NFPA does not yet require Approved/Listed devices for flow-rate measurement in either fire flow testing or fire pump testing. Standards tend to shy away from requiring a particular product to be used.