901003 100796 PDF

901003 100796 PDF
OPER
ATING
OPERA
INSTRUCTIONS
Volumetric Pressure Plate Extractor and Hysteresis Attachments
04/2005
1270
Heater Block
1250 Extractor
Disassembled
1250 Extractor
1250 OPERATING INSTRUCTIONS
Unpacking ........................................................................................................................ Page 1
Acquaint Yourself with the Parts ................................................................................... Page 2
Model 1275 Hysteresis Attachments .............................................................................. Page 3
Air Pressure Sources .......................................................................................................Page 4
Making a Run for Moisture Determination ...................................................................Page 6
Making a Run for Hysteresis Studies .............................................................................Page 8
Making a Run to Establish Moisture Retention Curves .............................................Page 12
General Care and Maintenance ....................................................................................Page 12
Replacement Parts ......................................................................................................... Page 12
Accessory Items ..............................................................................................................Page 12
1
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
MML008 *
Lab Stand
& Clamps
1276 *
Vapor
Saturator
1270
Heater Block
MGL001 *
Burrette
1277 *
Air Trap
MRT003 *
Tubing
1278 *
Ballast
Tube
0776L60
Connecting Hose
MRT012 *
Tubing
MRT007 *
Tubing
THE MODEL 1250 VOLUMETRIC PRESSURE PLATE
EXTRACTOR is a precision extractor designed so that
the outflow section of the instrument is stable dimensionally. When the extractor is used in conjunction with
the Hysteresis Attachments, the volume of water removed from the sample at each increasing pressure step
can be accurately measured and retained. When pressure values are subsequently reduced, the volume of
water that returns to the soil can then also be accurately measured.
By this means, one can investigate the hysteresis properties of the soil. The Volumetric Pressure Plate Extractor in conjunction with the Hysteresis Attachments also
makes it possible to measure the capillary conductivity
of soils. The extractor can, of course, be used for any
routine moisture extraction work on disturbed samples
or undisturbed soil cores.
UNPACKING
When unpacking your Volumetric Pressure Plate Extractor, carefully remove all packing material and tape,
and check for any damage that may have occurred during shipment, especially to the Porous Ceramic Plate.
NOTE: ANY DAMAGE FOUND UPON RECEIPT
SHOULD BE REPORTED IMMEDIATELY TO THE
TRANSPORT CARRIER FOR CLAIM. IT IS IMPORTANT THAT YOU SAVE THE SHIPPING CONTAINER
AND ALL EVIDENCE TO SUPPORT YOUR CLAIM.
Be sure to read all operating instructions thoroughly
before operating the extractor.
For full range operation, the extractor requires a source
of carefully regulated air pressure with a range of 0 to
30 psi (2 Bars or 200 kPa).
2
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
ACQUAINT YOURSELF WITH THE PARTS
CONSTRUCTION DETAILS
The extractor incorporates a 2 bar porous ceramic plate
which permits the operation of the extractor at any pressure between 0 and 2 bars (30 psi).
Fig. 3 shows a cutaway view of the extractor. The three
operating sections of the unit are held together by four
clamping bolts and wing nuts. In breaking the unit down
for loading, it is only necessary to loosen the four wing
nuts and slip the clamping bolts out of their slots. You
will note that the clamping bolts have square sections
at the head of the bolt which fits into the constraining
groove in the base plate. This prevents the bolts from
turning when the wing nuts are tightened or loosened.
The porous ceramic plate has been carefully ground and
fitted to the base plate so that there is a minimum space
for entrapment of air. Five symmetrically machined
grooves in the base plate, beneath the porous ceramic
plate, provide channels for the outflow of moisture from
the extractor to the two outlet tubes on opposite sides of
the base plate.
The cylinder of the extractor contains the pressure inlet
fitting to supply regulated pressure to the extractor. The
cylinder is sealed to the base plate and the top plate
when assembled by “O” ring seals which are snugly fitted into the grooves in the ends of the cylinder. The “O”
ring seals assure a reliable pressure seal requiring only
moderate clamping force on the wing nuts.
Two tapped holes in the cover of the extractor are provided to accept the Heater Block. If one is conducting
long-run, precise experiments, such as in the investigation of the hysteresis properties of soils, errors can be
introduced by moisture condensing on the inside walls
of the extractor due to temperature differences between
the soil sample in the extractor and the walls of the extractor. This can be avoided by conducting the work in
a temperature-controlled laboratory room. If this is not
available, one can mount the Heater Block. The Heater
Block operates on 12 volts AC or DC and puts out 3
watts of heat. This small source of heat maintains the
walls of the extractor at a slightly higher temperature
than that of the soil sample, and eliminates condensation on the inside walls of the extractor.
3
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
The Heater Block is ordered separately as an accessory
item.
UNIT SPECIFICATIONS
Pressure Rating:
2 Bars (30 psi)
Ceramic Plate Working Diameter: 4.69 in. (1 1.7 cm)
Ceramic Plate Thickness: .32 in. (.81 cm)
Ceramic Plate Conductivity: K = 6.30 x 10-7 cm/sec.
Overall Dimensions:
Height: 6 inches (15.3 cm)
Width: 5-7/8 inches (14.9 cm)
MODEL 1275 HYSTERESIS ATTACHMENTS
The Hysteresis Attachments have been designed specifically to operate with the Volumetric Pressure Plate
Extractor. The purpose of the Hysteresis Attachments
is to accurately retain all of the moisture removed from
a sample during the extraction process and to permit
the backflow of moisture from the storage area into the
sample as extraction pressures are reduced. The attachments therefore, provide a means of accurately determining the moisture removed from a sample at progressively increasing pressure steps for comparison to the
moisture absorbed by the sample as the pressure is successively reduced. This process corresponds to the drying and wetting cycle that occurs in soils in the field.
From the information obtained, one can delineate the
hysteresis effects of various soils.
Because of the extreme accuracy with which moisture
removal and uptake can be measured with the Volumetric Pressure Plate Extractor in conjunction with the
Hysteresis Attachments, the apparatus also makes it
possible to measure the unsaturated capillary conductivity of soils.
AIR TRAP
The Air Trap, see Fig. 5, fabricated from glass, provides
a place for collection of air that may defuse through the
porous ceramic plate in the extractor or which may come
out of solution in the water during a run. The “level
mark” on the stem of the Air Trap provides a convenient reference point to set the water level before reading the amount of water removed from a sample during
a run.
The various parts of the Hysteresis Attachments are pictured and identified in Fig. 2 by an asterisk (*).
VAPOR SATURATOR
Air enters through the Vapor Saturator. Prior to use,
the bowl of the saturator is unscrewed from the cap and
partially filled with water, see Fig. 4. The bowl is then
replaced. The purpose of the saturator is to completely
saturate incoming air to the Volumetric Pressure Plate
Extractor so that there will be no drying effect on the
soil sample being tested, so that no errors will be introduced into the water volume measurement from this
source. The Vapor Saturator is designed for operation
at pressures up to 30 psi.
4
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
ADDITIONAL HYSTERESIS EQUIPMENT
In addition to the glass parts, the Hysteresis Attachments include a suitable laboratory stand and assortment of laboratory clamps to support the various operating parts of the attachments, see Fig. 2.
The interconnecting rubber tubes to link up the various
parts, as indicated in Fig. 2, are also supplied.
BALLAST TUBE
The Ballast Tube, see Fig. 6, fabricated from glass, provides a horizontal storage area for water flowing in or
out of the soil sample within the extractor. Because the
Ballast Tube is in a horizontal position the outflow of
moisture or uptake of moisture does not change the hydraulic pressure relations existing within the soil sample
during the extraction process.
The Ballast Tube is positioned either at the center line
of the soil sample or at the base line of the soil sample,
depending upon the requirements of the test being run.
A “level mark” on the upturned end of the Ballast Tube
provides a reference point for setting the water level
when outflow or uptake volume measurements are being made.
AIR PRESSURE SOURCES
EXISTING LABORATORY AIR SUPPLY AS SOURCE
The input pressure can be from a laboratory supply line
which delivers pressure of 50 psi or higher. For accurate extraction work, it is essential to have a well regulated pressure. Our Model 0700G3 Manifold is normally
used to provide regulated pressure to the Volumetric
Pressure Plate Extractor, see Fig. 7. The Model 0700G3
Manifold provides regulated pressure in the range from
0 to 60 psi with accuracy of regulation within 1/100 psi
of the set value. The maximum input pressure to the
Model 0700G3 Manifold is 400 psi.
Thread size on the Model 0700G3 Manifold fittings are
1/4 NPT pipe thread, which is a U. S. standard pipe
size. Where you are providing hose connection from a
laboratory supply line you may need to replace the inlet
fitting of the Model 0700G3 Manifold. Our current price
list carries a number of adapters that may suit your requirements. Our Model 772G02 Adapter converts the 1/
4 NPT inlet thread to a 1/4" I.D. hose size.
BURETTE
The Burette shown in Fig. 2 provides a storage place for
water. When measurements are made after equilibrium
is reached, the height of the liquid within the Burette
indicates precisely the amount of moisture removed or
added to the soil sample within the extractor.
5
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
LABORATORY COMPRESSOR AS SOURCE
The input pressure can be from our Model 0500 Series
PM Compressors which are designed to provide a source
of pressure for all of our extractors, see Fig. 8.
The Model 0700G3 or the Model 0750G3 Pressure Control Manifold may also be purchased as part of a combination pressure control manifold, such as the Model
0700CG123 or 0750CG123, used where several different types of extractors are operating together.
CAUTIONS OR WARNINGS
Be sure seating area of “O” rings are clear of soil particles before assembling the extractor. Check to see that
the top plate is set firmly in place, with the bolts and
wing nuts seated properly. Inspect for wear on the
threads and bolts, then tighten until a good seal is made.
The regulated pressure supply must always include an
accurate pressure gauge to register pressure within the
extractor.
Increase pressure gradually and carefully, preventing
the possibility of over-pressurizing the unit.
PRESSURIZED AIR CYLINDER AS SOURCE
If air from a compressor is not available and one is obliged
to operate from high pressure compressed air or nitrogen in tanks, our Model 0750G3 Manifold can be used.
Accuracy of pressure regulation from this source is not
as accurate as from our Model 0700G3 Manifold. From
the Model 0750G3 one can expect variations of pressure
in the low pressure range of approximately 1/10 to 2/10
psi from the set value. Fig. 9 shows a schematic view of
the laboratory setup.
MAKING A RUN FOR PERCENT MOISTURE DETERMINATION
In making a run with the Volumetric Pressure Plate
Extractor, soil samples are handled in the same manner as for other pressure plate extractors.
Undisturbed soil cores should be trimmed flat so that
they make good contact with the ceramic plate.
Disturbed or loose soil samples should be prepared in
conformance to recommendations by the United States
Department of Agriculture as outlined below:
The soil is passed through a 2 mm round hole sieve with
the aid of a rubber stopper. One purpose of such sieving
is to remove rocks larger than 2 mm; another is to reduce all aggregates to less than 2 mm. In the removal of
rocks between 2 mm and 6 mm, they may be returned
to the screened sample if desired. The entire sub-sample
is then placed on a mixing cloth and pulled in such a
way as to produce mixing. Some pulling operations will
produce segregation instead of mixing, and special care
must be exercised to obtain a well mixed sample. The
soil sample is then flattened until the pile is 2 to 4 cm
deep.
For moisture retentivity, hydraulic conductivity, and
modulus of rupture tests, 2 to 6 sub-samples, each having a fairly definite volume, are required. Use paper cups
to hold the individual sub-samples. Mark with a pencil
line around the inside of the cup the height to which the
cup is to be filled to give the correct amount of subsample. Then, using a thin teaspoon or a small scoop,
6
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
lift small amounts of soil from the pile, placing each in
successive cups and progressing around the pile until
the cups are filled to the desired level. It is difficult with
some soils, especially if they have been passed through
a 2 mm round-hole sieve, to take samples from the pile,
without allowing the larger particles to roll off the spoon
or scoop. This roll back should be avoided because it
makes the extracted sub-sample non-representative. The
rollback problem is practically absent from some soils,
especially if all the sample has been passed through an
0.5 mm sieve.
Undisturbed soil cores or prepared soil samples must be
appropriately retained by a Soil Sample Retaining Ring
or other cylinder, see Accessories on Page 12, so that
they can be supported on the porous ceramic plate of
the extractor. After the sample is mounted on the porous ceramic plate, see Fig. 10, an excess of water is
allowed to stand on the plate so that the samples can be
soaked with water for at least 16 hours until they are
fully saturated. The reservoir formed by the clamping
ring of the extractor is convenient for retaining water
during this soaking period.
After the soaking period, excess water on the plate can
be removed by a syringe or plastic spout top bottle.
The cylinder and top plate of the extractor are then
mounted so that air pressure can be applied to the extractor. Care should be taken to clear any soil particles
from the seating area of the “O” rings prior to assembling the cylinder and top plate.
If the purpose of the run is simply to bring the soil sample
to some known moisture content such as 1/3 bar, I bar
or any specific value between saturation and 2 bars, then
the air pressure within the extractor is set at the desired value. Setting the pressure at 4.8 psi (1/3 bar) will
cause moisture to be removed from the sample until, at
equilibrium, the soil suction value within the sample
will be 1/3 bar. Likewise, setting the air pressure at 14.5
psi (1 bar) will cause moisture to be removed from the
sample until at equilibrium the soil suction value within
the sample will be 1 bar.
As soon as air pressure is applied, water will start dripping from the outlet tubes on either side of the base
plate, see Fig. 11. For this type of application, one of the
outlet tubes can be closed by a rubber stopper so that
the outflow comes from one tube. The water can be collected if desired in a burette so that the change in rate
of outflow can be observed. Initially, the flow from the
plate will be at a maximum and then will taper off as
equilibrium is approached. At equilibrium, there will be
no flow of water from the extractor.
If the soil samples in the extractor are 1 cm high, as
retained in our Soil Sample Retaining Rings, equilibrium on all types of soils will be reached within 48 hours.
Some soils will approach equilibrium in 18 to 20 hours.
In general, the time to reach equilibrium is a function
of the height of the soil sample as well as the conductivity characteristics of the soil. The time to reach equilibrium is proportional to the square of the height of the
sample. In other words, a sample 2 cm high would require 4 times as long to reach equilibrium as a sample 1
cm high. In any event, true equilibrium can be determined by the outflow of moisture, and when this ceases
equilibrium has been reached.
7
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
After equilibrium has been reached, the pressure is released and the extractor immediately opened and the samples
removed and placed in moisture boxes to prevent any further changes in moisture content. If the purpose of the
run is to measure the moisture content at the specific soil suction value, then the sample and moisture box would
be weighed. The sample would then be dried to constant weight at 105ºC. The loss in weight of the sample would
then be divided by the dry weight of the sample and the moisture content would be expressed as a percentage of
dry weight.
MAKING A RUN FOR HYSTERESIS STUDIES
After the soil sample has been prepared and fully saturated in the extractor, as indicated on Page 6, connections
are made to the various parts of the Hysteresis Attachment. This is shown in Fig. 2, and then further clarified in
Fig. 12 above, which shows a diagrammatic view of the arrangement.
For accurate hysteresis measurements, the extractor should be run in a temperature controlled room or you
should attach and operate the Heater Block. This is essential to keep moisture from accumulating on the inside of
the extractor walls and thus introducing an error in the measurement, as explained on Page 3.
Water is now added to the Hysteresis Attachments to fill the various connecting tubing and the Air Trap up to the
“level mark”. This is most easily accomplished by pouring a small quantity of water in the Burette. The stopcock
at the base of the Burette is then opened and the stopcock at the top of the Air Trap is opened so that water can
flow into the Air Trap and connecting tubing. Care should be taken to adjust the Ballast Tube so that water does
not flow out the end of the Ballast Tube during this initial filling operation. When water has reached the “level
mark” in the Air Trap, the stopcock at the base of the Burette and the stopcock at the top of the Air Trap are
closed.
8
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
Water is now circulated underneath the porous plate
within the extractor by running a roller over the connecting tube as shown in Figs. 12 and 13. Running the
roller over the connecting tube pumps water from the
Air Trap through the grooves in the base of the extractor, underneath the porous ceramic plate. This pumping action forces out air bubbles which then accumulate
in the Air Trap. When all the air has been removed, this
rolling (pumping) operation is stopped. The water is then,
again adjusted to the “level mark” of the Air Trap by
opening the stopcock at the top of the Air Trap and then
opening the stopcock at the bottom of the Burette so
that additional water can flow in until it reaches the
“level mark”. At this point the stopcock at the top of the
Air Trap is immediately closed and the stopcock at the
bottom of the Burette is closed.
10 bar, 1.45 psi, is applied to the extractor from the pressure supply manifold.
Once the pressure has been applied to the extractor,
moisture will begin to move out of the sample until the
first equilibrium value is established. As moisture is
removed, it will accumulate in the Ballast Tube. When
the Ballast Tube fills with water and outflow is still taking place from the extractor the existing water in the
Ballast Tube is pulled up into the Burette, as shown in
Fig. 14.
The height of the Ballast Tube is now adjusted so that it
is level with the top surface of the porous ceramic plate
of the extractor, or with the center line of the sample, if
this reference point is desired. To do this it may be necessary to elevate the extractor by placing it on a block of
wood or other support. The extractor is now closed.
CAUTION
The initial outflow of water may be of considerable volume if the soil sample being run is large. Attention must
be paid for the first few hours after the pressure is first
applied to make sure the Ballast Tube does not overflow.
Water remaining in the Ballast Tube should be removed
before applying pressure to the extractor. This is accomplished by applying a low vacuum at the top of the
Burette, see Fig. 14. Very little vacuum is required, and
this can be supplied by a conventional laboratory vacuum
line or by an air aspirator or by mouth. While the vacuum
is applied at the top of the Burette, the stopcock is carefully opened at the bottom of the Burette. Existing water then begins to move from the Ballast Tube up into
the Burette. When sufficient water has been brought
up into the Burette, the stopcock at the bottom of the
Burette is closed and the vacuum is removed.
The lifting of the water up into the Burette provides the
additional volume needed to take care of additional outflow of moisture from the soil sample.
In order to establish a starting point for the soil moisture hysteresis attachments, a low pressure such as 1/
When outflow of moisture from the sample has completely ceased, as determined by a stoppage of water
flowing into the Ballast Tube, then equilibrium has been
reached.
Before making a reading, several adjustments need to
be made.
First, purge any accumulated air from the grooves underneath the porous ceramic plate. This is done by run-
9
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
ning a roller over the connecting tube as shown in Figs.
12 and 13, and as explained earlier. During a run, air
tends to accumulate in the grooves underneath the porous ceramic plate. This air accumulation would introduce errors in the liquid volume measurement if not
removed. Air accumulation under the porous ceramic
vacuum will pull water out of the Ballast Tube up into
the Burette. When the water reaches the “level mark”
in the Ballast Tube, the Burette stopcock is closed and
the vacuum is removed.
The volume reading in the Burette at the first equilibrium value is now noted down. This will then be the
starting point for all future measurements of moisture
removed from the sample during the run.
plate would also tend to prevent liquid uptake by the
sample in experiments where air pressure is reduced
after equilibrium is reached. Running the roller over
the connecting tube purges accumulated air which collects in the Air Trap.
Next, adjust the water in the Air Trap to the “level mark”,
see Fig. 15. If water in the Air Trap is below the “level
mark”, apply a vacuum to the outlet stem of the Air
Trap and carefully open the stopcock on the Air Trap
until the water rises to the “level mark”. Then close the
stopcock and remove the vacuum.
The water level in the Ballast Tube is now adjusted to
the “level mark”, see Fig 16. If the water level is below
the “level mark”, the stopcock on the Burette is carefully opened to allow water from the Burette to flow into
the Ballast Tube up to the “level mark”. The stopcock is
then closed. If the water level in the Ballast Tube is
above the “level mark”, then a low vacuum is applied to
the top of the Burette before the stopcock is opened.
When the burette stopcock is carefully opened, the
After the establishment of the starting volume value on
the burette, pressure within the extractor is raised to
the next desired value. As soon as the pressure is raised
within the extractor, moisture will then flow from the
soil sample and collect in the Ballast Tube. Where you
are removing moisture from the soil sample at successively increasing pressure values, you must make provision for the outflow of additional water by pulling water
from the Ballast Tube up into the Burette. In other
words, after you have made the equilibrium volume reading on the Burette, you again apply vacuum to the top
of the Burette, open the stopcock at the bottom of the
Burette and pull water from the Ballast Tube up into
the Burette, and then close the stopcock at the bottom
of the Burette. This procedure provides a volume within
the outflow system for the accumulation of additional
water from the soil sample, see Fig. 17.
Again, after equilibrium at the new pressure value is
reached, as indicated by the stoppage of additional water flowing into the Ballast Tube, the water within the
outflow system is adjusted up to the “level mark” on the
10
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
ter level has been established at these two “level marks”,
the volume at the Burette is read and recorded. The
decrease in volume in the Burette is an exact measurement of the amount of water that has moved back into
the sample as a result of the decrease in pressure within
the extractor.
Air Trap on the Ballast Tube, as indicated earlier. A
new volume measurement is then made on the Burette,
and recorded. The change in volume, as indicated by
the two measurements on the Burette, indicate precisely
the amount of moisture that was removed from the soil
sample between the two equilibrium air pressure values applied to the soil sample in the extractor.
This process is repeated at increasing pressure values
until the desired range in pressure is covered.
At the close of the run after the last equilibrium value
has been established and Burette reading recorded, the
pressure in the extractor is released, and immediately
opened, and the complete soil sample immediately removed and transferred to a conventional moisture box
and weighed. The complete soil sample is then oven dried
at 105ºC, until no further loss of weight occurs.
The sample is again weighed. The moist weight of the
sample at the last equilibrium value is then compared
to the dry weight of the sample so as to develop the moisture percentage in the sample at the last equilibrium
value. The changes in the volume of water removed from
the sample as developed by the volume readings on the
The reverse process can now be carried out. In this case,
the pressure within the extractor is now reduced. When
the pressure in the extractor is reduced, water will begin to flow back into the sample from the Ballast Tube.
This backflow of moisture into the sample can be noted
by the movement of the water meniscus in the Ballast
Tube. When movement of water from the Ballast Tube
has ceased, a new equilibrium at the lower pressure has
been reached.
During the backflow of moisture into the sample, more
water may be required than is stored in the Ballast Tube.
To add more water to the Ballast Tube, simply open the
Burette stopcock and allow water flow into the Ballast
Tube up to the “level mark”. See Fig. 18.
When equilibrium is reached, the water is again adjusted
to the “level mark” on the Air Trap and the “level mark”
on the Ballast Tube as described earlier. After the wa-
11
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
Burette during the course of the run permit you to determine accurately the moisture percentage within the
soil sample at each of the equilibrium values established
during the run. The percent of moisture is then plotted
against the equilibrium pressure values. Fig. 19 shows
the hysteresis effects in Aiken Clay Loam as developed
from measurements with the Volumetric Pressure Plate
Extractor.
Madison, Wisconsin 53711, U.S.A.
Sections 16 and 17 of this publication describe the measurement of hydraulic conductivity of unsaturated soil,
and the measurement of water diffusivity, which is
closely related.
MAKING A RUN TO ESTABLISH MOISTURE RETENTION CURVES
The extractor is ruggedly built and requires little in the
way of maintenance. “O” ring seals and clamping bolts
may need replacement over a long period of time. These
are available and listed below and along with the Extractor on our current price list.
The Volumetric Pressure Plate Extractor can be used to
develop accurate moisture retention curves on all types
of soils in the 0 to 2 bar range.
A moisture retention curve, or moisture characteristic
as it is sometimes called, is the relationship of the moisture content of the soil to the soil suction value at which
the moisture is held. Typical moisture retention curves
for 3 types of soils are indicated in Fig. 20.
The procedure for developing moisture retention curves
is identical to that used for measuring the hysteresis
effects with the exception that the equilibrium values
are established only at increasing pressure equilibrium
values within the extractor.
MEASUREMENT OF HYDRAULIC CONDUCTIVITY
OF UNSATURATED SOILS
The Volumetric Pressure Plate Extractor is suitable for
measurement of hydraulic conductivity in unsaturated
soils by the Unsteady State Method. This procedure is
best described in the following publication:
Methods of Soil Analysis
Agronomy No. 9, Part I
Available from:
American Society of Agronomy
677 South Segoe Road
GENERAL CARE AND MAINTENANCE
Care of the Volumetric Pressure Plate Extractor
To prevent evaporation deposits on the porous ceramic
plate of the extractor, which will slow down the flow
rate, it is recommended that after a run the extractor is
wiped dry of moisture and then a small quantity of a
fine sandy loam soil may be placed on the porous ceramic plate of the extractor. The base of the extractor is
then allowed to air dry. Moisture from the porous ceramic plate will move into the fine sandy loam during
the drying process and any salt deposits will be made in
the fine sandy loam rather than on the surface of the
porous ceramic plate. After thorough drying, the soil on
the plate can then be removed and the extractor closed
for storage.
REPLACEMENT PARTS
Model No.
Description
M802X251
“O” Ring, Cylinder Seal
1252
Clamping Bolt Assembly
1253B02M1
Porous Ceramic Plate, 2 Bar
1254
Gasket, Ceramic Plate Seal
1276
Vapor Saturator
1277
Air Trap
1278
Ballast Tube
MRT003
Neoprene Tubing, 3/16" I.D. X 1/8" wall
MRT012
Neoprene Tubing, 1/8" I.D. X 1/16" wall
ACCESSORY ITEMS
PART NO.
DESCRIPTION
0206L06
Cylinder, 2-1/4" O.D. X 6 cm long
0206L03
Cylinder, 2-1/4" O.D. X 3 cm long
0206L01
Cylinder, 2-1/4" O.D. X I cm long
0700G3
Manifold
0750G3
Manifold
0772G02
Adapter, 1/4 NPT male pipe to ¼" I.D.
hose
1093
Soil Sample Retaining Rings, 1 dozen
1270
Heater Block & Mounting Screws
1275
Hysteresis Attachments
0776L60
Connecting Hose, 40" long
1426L6
Cylinder, 3-1/2" O.D. X 6 cm long
1426L3
Cylinder, 3-1/2" O.D. X 3 cm long
12
SOILMOISTURE EQUIPMENT CORP.
P.O. Box 30025, Santa Barbara, CA 93130 U.S.A.
Phone: (805) 964-3525 - Fax: (805) 683-2189 - Email: sales@soilmoisture.com
Website: http://www.soilmoisture.com
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