There are two main types of pressure gauges we see used in water related industries, the Manometer style gauge and the Bourdon style gauge. The most common in irrigation is the Bourdon type. These are the common pressure gauges you frequently see; they feature a needle and dial enclosed within a housing and lens. All of the pressure gauges we currently carry are Bourdon types. Bourdon type gauges are significantly easier to use, read, and do not need frequent calibration.
How Pressure is Measured
There are many units of measurement in regards to pressure, however in irrigation you will mostly run into two primary ones: PSI and Bar. PSI is the imperial measurement and mostly what we deal with here in the states. Bar is the metric equivalent (but not part of the International System of Units) and is seen in most other locations. Many pressure gauges will feature both Bar and PSI on the needle dial. One Bar is equal to 14.50 PSI. Pascal will sometimes be seen as well, as it is the standard SI unit of measurement.
Why and Where to Test Pressure?
The reasons to test pressure are myriad, and many depend on where you're testing the pressure. For example, testing the pressure at the spigot will be done for different reasons than testing pressure across a filter, or at the end of a lateral line.
Testing the Water Source
Testing the pressure of the water source is one of the first and most important steps that will be taken when designing an irrigation system. This gives you the starting pressure of your system, and serves as the baseline from which other calculations will be done. Testing the pressure of the water source also helps identify compatible pressure regulators (or if one is even needed at all!) and emitters.
Filter and Venturi Injectors
I grouped these two together as pressure is often tested at these for the same reason: to detect and determine pressure differential. In regards to the filter, testing pressure at both the inlet and outlet can determine the pressure differential which can inform of potential problems such as a clogged filter.
Venturi injectors actually rely on pressure differential in order to work and inject treatments into the irrigation system. For Venturi injectors, pressure differential is required. If your Venturi injector is not working, testing the pressure differential can quickly diagnose the cause.
Lateral Lines and Emitter Line Rows
At the ends of laterals, emitter line rows (drip tape or drip line) are common places to test pressure. Knowing the pressure at the end of a run is important in regards to distribution uniformity. If pressure is particularly low at the end of an emitter line run, the emitters at the end of that run may not be delivering the same volume of water as at the start of the run. If this discrepancy is large enough, under-watering the plants at the end, or over-watering the plants at the start of the run could occur.
Liquid Filled and Dry
While all of our gauges are Bourdon types, there are some important differences. The first thing you’ll notice is that some pressure gauges are liquid filled and some are not. This one is not a case where one is always better than the other, as it largely depends on application.
Liquid filled pressure gauges are slightly more accurate in most (but not all) cases. The liquid serves to reduce vibrational influence on the pressure reading. Anyone who has pressurized an irrigation system can attest to the amount of vibration encountered in the pipe, fittings and other components. Liquid filled pressure gauges are also more durable when used in an outdoor location where temperatures can drop below freezing. In a dry gauge, moisture in the form of condensation can build up inside the gauge, and when temperatures fall, that condensation can freeze and cause damage to the gears inside of the unit.
Again, the viability of one over the other is largely in application; a low pressure, indoor greenhouse grow may not have enough vibration to influence readings and is unlikely to fall below freezing, meaning a dry pressure gauge could serve just as well as a liquid filled one.
Another difference between our pressure gauges is in mounting type. Some gauges mount via a ¾” female hose connection, another via a ¼” male pipe thread connection, and even one that takes reading through a pitot tube and another via a Schrader valve. The different mount types tend to be used in different locations.
¾” FHT Mount
The gauges with a ¾” female hose threaded mount are often used at the end of the mainline, laterals or even emitter line (drip tape or drip line) rows. Perma-Loc end caps, if the cap is removed, have male hose threads where the regulator can be attached to test pressure at those locations.
¼” MPT Mount
Our gauges with a ¼” male pipe threaded mount are most frequently used at the filter. One gauge is attached to the inlet side of the filter, and another is attached to the outlet. This allows the pressure differential between the two points to be measured, which can indicate issues such as a clogged filter.
Pitot tube pressure gauges are often used to spot check pressure in various locations, typically (but not limited to) the lateral lines. To use a pitot tube pressure gauge, you can simply punch a small hole in the tubing and insert the pitot tube into that hole to take a pressure reading. After this is complete, the hole can be filled with a goof plug. This method works well to audit pressure at various locations in the system and can be done at a sprinkler head as well by letting the stream hit the pitot tube.
Pressure gauges equipped with a Schrader valve adapter can check pressure at fittings, adapters and other items that have a Schrader valve. You’ve likely seen these on bicycle and automobile tires and likely tested air pressure using one; the same concept applies in irrigation. These can be strategically placed at various points in the system where checking pressure is important.
Female Nozzle Adapter Mount
Some gauges come with male adapters compatible with female nozzles in spray bodies. This allows each spray head to be tested individually, something invaluable when it comes to troubleshooting problematic spray heads.
|Underhill GHT Liquid Filled Pressure Gauge|
|Irritec Liquid Filled Pressure Gauge|
|Irritec Liquid Filled Pressure Gauge||X||0-100||0-7||1/4" MPT|
|Underhill Pressure Gauge w/ Pitot Tube||X||0-160||0-10.5||Pitot Tube|
|Aqualine Dry Pressure Gauge||X||0-200||3/4" FHT|
|Aqualine Liquid Pressure Gauge||X||0-200||3/4" FHT|
|Underhill Pressure Gauge w/Schrader Valve||X||0-160||0-10.5||Schrader Valve Adapter|
|Irritec Dry Pressure Gauge||X||0-100||0-7||3/4" FHT|
|Underhill Pressure Gauge for Spray Bodies||X||0-160||0-10.5||Adapter for Female Nozzles|