digital pressure gauges

Analog models don’t provide the same benefits when faced with variable pressures, multiple units of measure, and extreme conditions

Out-of-date pressure gauges are some of the most common fire code violations in fire sprinkler and standpipe systems. That’s hardly surprising—there are simply a lot of them. They’re everywhere, connected to equipment and components as varied as fire pumps, sprinkler system piping, hydrostatic test pumps, and flow-testing pitot gauges.

Most such gauges are “analog.” They use springs, tubes, and a complex arrangement of other mechanical parts to measure pressure. But these traditional, clock-like gauges face competition from a modern alternative: handheld digital pressure gauges. And while both have their place in standpipe and fire sprinkler inspection, testing, and maintenance (ITM), electronic pressure instruments can:

  • Simplify tests and inspections
  • Assist in gauge calibration
  • Provide legible readings in poorly lit spaces
  • Reduce the number of devices contractors need to perform their duties effectively

To learn how, read on.

If you’ve come across this article while searching for a digital pressure gauge—or if you want to compare the specifications for yourself—take a look at our DG25 Digital Air/Water Pressure Gauge and our selection of analog pressure gauges.

From flow tests to monitoring “ultra-high-speed” fire suppression systems, gauges are essential in standpipe and fire sprinkler inspection, testing, and monitoring

Some of the most recognizable gauges in water-based systems indicate the pressure of the water supply—or the pressure just inside the system. However, others are used for more localized or specific tasks, like assessing changes in pressure as the fire sprinkler system is drained.

At critical valves, drains, and pipes, these compact devices make required standpipe and fire sprinkler inspections easier. Their readings streamline routine check-ups and professional tests alike, providing indications of a leak, obstruction, or malfunction. In fire sprinkler systems, air and water pressure gauges might be found at:

Gauges on fire sprinkler risers

At least seven gauges are visible in on these fire sprinkler system risers—and more may be obscured from view. Source: Fire Tech Productions, Inc.

In standpipe systems, air and water pressure gauges regularly measure the water pressure of a wet-pipe system or the gas pressure of a dry-pipe system. They’re also attached to alarm valves and are used as part of dry-pipe valve trip tests, as well as in tests of pressure-reducing valves.

Replacement is often favored over recalibration, making digital pressure gauges less common than their analog counterparts

For more on the use and care of these devices—along with a hefty list of other ITM tasks—fire professionals consult NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. One requirement in NFPA 25 often leads installers and facility managers to treat gauges as disposable.

From the 2017 edition of NFPA 25

13.2.7.2* Gauges shall be replaced every 5 years or tested every 5 years by comparison with a calibrated gauge.

13.2.7.3 Gauges not accurate to within 3 percent of the full scale shall be recalibrated or replaced.

This section doesn’t mandate a replacement. However, many installers favor low-cost analog gauges that generally remain accurate long enough to comply with this requirement—and can be quickly disposed of every five years.

An out-of-date gauge

While it’s possible that this gauge has been recently tested, this analog device is more than 15 years old and doesn’t show evidence of recalibration. Source: Fire Protection Deficiencies

However, for those that choose recalibration, NFPA 25 doesn’t demand that inspectors test and recalibrate each gauge individually. Minnesota’s State Fire Marshal notes that pressure gauges “installed in similar positions and elevations (e.g. on an adjacent riser)” may do the trick, so long as they remain accurate to within +/- 3% of the gauge’s full scale. If, for example, a 100 PSI gauge is placed under 50 PSI of pressure, NFPA 25 allows that gauge to remain in service as long as the readings range from 47 to 53 PSI (50 +/- 3).

Handheld digital pressure gauges play a supporting role, providing a reference for analog gauge calibration

In the middle ground between replacing every gauge and recalibrating every gauge is a hybrid of the two approaches. Inspectors can quickly test installed gauges, replace or recalibrate devices that fail, and mark the date of testing. The NFPA 25 Handbook reduces testing to a five-step process:

  • Notify responsible parties (e.g. fire officials, building owners) that testing will begin
  • Install the testing gauge in the (closed) outlet of a pressure gauge connection (again, typically a three-way valve)
  • Open the valve and note the readings; then, close the valve and remove the gauge
  • Repeat this process with the gauges to be tested
  • Notify parties that testing has completed.

Afterward, contractors can recalibrate or replace any gauges that fall outside of NFPA 25’s acceptable range. Notably, there’s nothing in the standard that specifies the use of a digital or an analog gauge as a reference for recalibration. But the NFPA 25 Handbook does mention that gauge accuracy tests should be performed with “test-quality gauges,” which:

  • Have an accuracy of +/- 1%
  • Are protected from rough handling
  • Receive annual calibration (or more often) with a testing machine

Many analog gauges that are well-suited for use in fire sprinkler systems are accurate to 2% or 3% of their overall range. That accuracy may vary in a single device, with better readings in the mid-range (from 25-75% of span) than outside of it.

Buy pressure gauges

From 25 to 75 PSI—where thin lines on the gauge face are visible—this analog gauge provides 1% accuracy.

By comparison, digital pressure gauges tend to deliver higher levels of accuracy across their full scale. In one of the few explicit mentions of digital pressure gauges, NFPA 25 notes that digital gauges may have several advantages specific to tests of fire pumps:

A.8.3.7.1 … Pressure gauges should have an accuracy not greater than 1 percent of full scale. To prevent damage to a pressure gauge utilizing a Bourdon tube mechanism [analog gauges], it should not be used where the expected test pressure is greater than 75 percent of the test gauge scale. Some digital gauges can be subjected to twice the full scale pressure without damage.

Fire pumps, the system riser, and other components produce different levels of pressure—and users of test gauges, whether analog or digital, need to keep that in mind. But digital pressure gauges can pair full-range accuracy with greater durability outside of that expected range, making errors less likely and less costly.

Digital pressure gauges can simplify fire protection math

Some handheld digital pressure gauges allow users to switch between different units of measurement. For example, the DG25—manufactured by the Connecticut-based Ashcroft, Incorporated—can display readings in nine different units:

  • PSI
  • Bar
  • Inches of mercury (in Hg)
  • Centimeters of mercury (cm Hg)
  • Millimeters of mercury (mm Hg)
  • Kilopascals (kPa)
  • Megapascals (MPa)
  • Kilograms/square centimeters (kg/cm squared)
  • Feet of water (ft H2O)

These units will come in handy for fire professionals tasked with performing a variety of inspections on water-based systems. The NFPA 25 Handbook, for example, includes a sample form for testing a centrifugal fire pump. These complex tests involve evaluations of suction, discharge, flow rates, and other factors that assess pumps’ capabilities. While most measurements are recorded in pounds per square inch—including the net pressure, oil pressure, and more—the exhaust backpressure is one of few units measured in inches of mercury.

Mercury barometer

While the use of mercury has fallen out of fashion, the unit of measurement lives on—and still proves useful in barometric and fire protection applications. Source: Paul VanDerWerf via Flickr

ITM professionals whose work extends beyond standpipe and fire sprinkler inspections may find this feature especially convenient. Formulas for the evaluating flow and friction loss in hose may use kPa rather than PSI. Negative pressure on a fire engine’s pumps may be easier to read in inches of mercury. And internationally sourced equipment may provide standard measurements in metric forms that aren’t convenient for American users. In short, inspectors and other users in the fire protection industry may find that calculations are simpler (and slightly less error-prone) with handheld digital pressure gauges.

Electronic pressure instruments combine the best traits of analog gauges with modern features to enhance ease of use

All of these features help to ensure that standpipe and fire sprinkler inspections go well and quickly. But there are “softer” benefits—small conveniences—that give handheld digital pressure gauges an edge. Contractors engaged in standpipe and fire sprinkler inspection, testing, and maintenance may also benefit from electronic models’:

Readability. Fire protection gauges aren’t always easy to read. Poor lighting, accumulated filth, leaks, and other issues can leave analog models nearly illegible. Digital pressure gauges combat these shortcomings in a few ways. Chief among those features is backlighting, which illuminates the digits shown on the dial for a pre-set length of time. And the numbers themselves may be far easier to read: on some Ashcroft models, each digit stands at roughly 1/2” tall on a gauge that’s just under 2 3/4” in diameter.

Memory storage. Most gauge inspections focus on two central questions: is the pressure too high, or is it too low? With an analog gauge, giving a precise answer to that question can be tough—especially during prolonged inspections or when equipment vibrates intensely. But some digital gauges can keep a record of those readings, storing minimum and maximum results for later review.

Flutter minimization. Depending on the gauge’s accuracy, the size of the dial, and the spacing of the numbers displayed, vibration may make taking accurate readings inconvenient or nearly impossible. But digital pressure gauges control how quickly readings update—basically hiding extreme flutter—to make getting better readings possible in challenging conditions. Compare that with an analog gauge, which may require a “pressure snubber” to keep gears inside the dial from slipping into misalignment (as this entertaining instructional video describes):

Visual features. A hand-and-dial-style gauge can’t offer the precision of electronic models. But it does make it easy to tell when a reading is too low, too high, or roughly in the middle of the gauge’s range. Digital gauges can simulate this feature with built-in graphs. These provide a quick way to ballpark when the reading falls in or out of the gauge’s overall range.

Bar graph on a digital gauge

These bar graphs (found on the left-hand side of each gauge’s LCD) fill as the gauge approaches the upper limits of its range. This model allows users to customize the upper and lower limits of that range, allowing it to act as several gauges in one.

Professional-quality gauges deliver in situations where precision matters

Electronic measuring instruments aren’t called for in every situation—but strong performance and convenience give fire protection professionals good reason to add handheld digital pressure gauges to their arsenals. If you’re in the market for a device meant to make inspections simpler, check out Ashcroft’s DG25 handheld pressure gauge. This gauge has a weatherproof rubber case, 0.5% full-scale accuracy, and approvals from:

  • CE (heavy industrial use)
  • ASME B40.7 (digital pressure gauges)
  • RoHS (environmentally suitable for use in European markets)
  • UL 61010 (electrical equipment for measurement)

This 0-300 PSI digital gauge can provide more than 2,000 hours of use with two AA-batteries, while toggling between units of measurement like:

  • Bar: 0-20.685
  • Inches of mercury (in Hg): 0-610.8
  • Centimeters of mercury (cm Hg): 0-517.2
  • Millimeters of mercury (mm Hg): 0-5172
  • Kilopascals (kPa): 0-689.5
  • Megapascals (MPa): 0-0.6895
  • Kilograms/centimeters squared (kg/cm2): 0-7.031
  • Feet of water (ft H2O): 0-230.77
Buy digital gauges

If cared for, the DG25 can endure 10 million pressure cycles (or more). Remember to loosen and tighten with a wrench—on the hex-shaped fitting only—and to prevent sudden pressure shocks with a bleeder valve.

View specifications for the Ashcroft DG25 Digital Pressure Gauge.

Questions? Call us at +1 (888) 361-6662 or email [email protected].

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