Product Manual

9
and especially if they continue over considerable periods, much more frequent servicing is required.
The maximum reading that can be reached is about 85. As this point is approached, a greater amount
of air is drawn into the instrument. In this range, the instruments should be “serviced” and the reservoir
should be filled, if necessary, about once a week. If servicing is not performed, eventually all the water
will be drawn out of the instrument and the vacuum will be lost, giving a “FALSE” zero reading.
For most field applications, less frequent refilling of the reservoir is required and satisfactory results
are obtained by “servicing” only when air is visible in the portion of the instrument above ground, after
gauge readings have dropped following an irrigation.
In research work, maximum accuracy and sensitivity are obtained if instruments are serviced every
few days. This practice is also recommended for field use under saline conditions, as it ensures that
almost all movement of fluid is outward. It thus reduces the amount of soluble salts drawn into the
instrument from the soil, following an irrigation.
Provided IRROMETERS are kept in an upright position, the fluid seal on the gauge prevents air from
entering the gauge, even though servicing is neglected for considerable periods. However, some air
may accumulate in the pores of the ceramic tips or on the walls of the plastic, so the hand vacuum
pump should be used in the field about every 30 to 60 days — particularly on instruments installed at
an angle — to ensure that the instruments are maintained entirely air free. Tapping the reservoir lightly
while the instrument is under vacuum from the pump helps to
release any air present.
Make sure that there is considerable soil moisture, at ceramic tip
depth, when using the hand vacuum pump and apply the vacuum
for only a few seconds. (Excessive vacuum applied when the soil is
dry, draws air into the instrument.)
Systematic servicing is essential to accuracy and quick response to
irrigations. If this is done just after charting readings, the extra time
required is almost negligible.
Hand Vacuum Pump
This pump has a universal suction cup that fits all standard size
models of the IRROMETER. Remove the IRROMETER filler cap
and apply the hand vacuum pump. Four or five quick strokes of the
piston will produce an 80 to 85 gauge reading, the maximum
vacuum. The pump will then adhere to the instrument “hands-off.”
This is a great convenience, as it leaves one hand free to release air
bubbles by tapping the main tube lightly.
Refer to “NOTES” on page
3 regarding LT, MLT and RSU IRROMETERS.
Always release the vacuum slowly so as to prevent shock to the
gauge movement. The suction cup of the pump has a built-in finger
release valve to facilitate slow release of the vacuum. Push the tip
of the release valve gently in any direction to bleed off the vacuum
slowly.
Periodic cleaning of the pump parts can be accomplished by
disassembling the pump and flushing all parts with clean water. After
drying, all parts, particularly the ball valve, should be lubricated with
a silicone lubricant spray.
NOTE: See “TEST PUMP” option on page 18.
Air removal
Release valve