EQUIPMENT & SUPPLIES: Samplers--P-61 and P-63 Point-Integrating Sediment Samplers
In Reply Refer To: November 19, 1979
EGS-Mail Stop 412
QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 80.03
Subject: EQUIPMENT & SUPPLIES: Samplers--P-61 and P-63 Point-
Integrating Sediment Samplers
The purpose of this Memorandum is to remind those people who use
the P-61 and P-63 point-integrating samplers of one of the most
common causes of malfunction of these samplers. If water gets into
the head cavity, corrosive damage to the plug and solenoid
assembly will cause the valve to stick and become inoperable if
proper maintenance procedures are not taken.
The valve which controls the nozzle and air openings is
electrically controlled, and has two positions (see Fig. 2). In
the power-off position the valve is in the pressure-equalizing
position; the nozzle is closed, and air flows only from the
compression chamber into the head cavity and from the head cavity
into the bottle. This equalizes the pressure in the bottle with
the hydrostatic pressure as the sampler is lowered through the
water. In the power-on position the valve is in the sampling
position; the nozzle is open, and the air flows only from the
bottle into the head cavity and out through the air-exhaust
opening.
Water can get into the head cavity under the following conditions
if: (References are to the enclosed drawings and parts list)
l) no nozzle is in place. Water will rapidly fill the head cavity
if a nozzle has not been properly installed.
2) the nozzle gasket is missing. Water will enter between the
nozzle and nozzle nut.
3) the sampler is submerged without a sample container in the
sampler. If the sampler is submerged without a container, water
can enter the head when the valve is in the power-off position. In
this position water can enter through the air-exhaust opening
(Section B-B). Solution--never submerge a sampler without a bottle
properly sealed in place.
4) the sample container is filled to the maximum recommended
volume and the sampler is allowed to tilt forward more than about
10 degrees after the valve has closed (power-off position). Some
water can run back through the air exhaust opening into the head
(Section B-B). If the sample container is overfilled water will
definitely enter the head cavity when the valve is closed (power
off). Solution--do not overfill the sample container. Try to keep
the sampler from tilting head down when retrieving and removing
the sample container.
5) the nozzle is not tightened into the valve body and the nozzle
nut is not tightened against the nozzle gasket (O-ring). The
nozzle (part P61-11) must be hand-tightened into the valve body,
then the nozzle gasket (P61-13) must be compressed by tightening
the nozzle nut (P6l-l2) to prevent water from entering the head
cavity around the nozzle. Solution--Loosen the nozzle nut before
inserting and tightening the nozzle, and then use an adjustable
wrench to tighten the nozzle nut gently against the O-ring.
6) the air-line gasket is worn or missing. The air-line gasket
(P61-29) is seated into the sampler head. When the head is closed
the gasket is pressed against the air-line opening in the body,
thus completing the air line from the compression chamber to the
head cavity and sealing it against leakage. If this gasket becomes
worn or damaged (or is missing), water can enter the head cavity.
Solution--The seal should be checked frequently by placing a paper
strip against the gasket and closing the head. If the paper strip
can be easily withdrawn, the gasket should be replaced before
submerging the sampler.
7) rinse water is poured onto the gasket and nozzle area of the
sampler head when the valve is in the power-off position. When
these samplers are used to collect samples for chemical analysis,
that part of the head which is in contact with the sample
container is supposed to be rinsed with native water at the
sampling site. If this is done while the sampler head is hanging
open with the valve in the power-off position (Section B-B), some
of the water that is poured onto the gasket and nozzle area can go
directly into the head cavity through the air-exhaust opening.
Solution--To rinse that part of the head and gasket which is in
contact with the sample container, l) place a proper container in
the sampler, 2) close the head, 3) submerge the sampler in the
stream to be sampled, 4) open the valve (power on), S) leave the
valve open long enough to fill the container about half full, 6)
raise the sampler to the point where the tail fin can be grabbed,
7) open the valve (power on) and tilt the sampler up and down to
rinse the contact area. Some water will be forced back through the
nozzle, but will not get into the head cavity as long as the power
is on. Discard the remainder and begin sampling.
It would appear that it is almost impossible to use these samplers
without allowing some water to get into the head cavity. It
definitely is difficult to prevent leakage; however, if care is
taken most problems associated with leakage can be minimized. If
the operator removes the nozzle and the nozzle nut after sampling
and opens the head while the sampler is in the suspended position,
excess water in the head will immediately drain through the
threaded nozzle-nut opening. Since air is free to flow through the
pressure-equalization hole near the hinge, if the sampler is
stored with the head open and the nozzle and nozzle nut removed,
the head cavity should dry within a few hours. A tire pump or
other compressed air source could be used to accelerate the drying
process.
Other points to remember are:
1, Disassemble the head and clean all parts frequently. If the
sampler is only infrequently used it should be cleaned following
each trip.
2. Be sure that the power supply is fully charged.
3. Make sure that there is direct contact between the hanger bar
and the Type B connector. Do not use a Type B connector with a
nylon bushing (See WRD Equipment Catalog, stock number 434003),
but do use the Type B connector with brass bushing (stock number
434002).
4. Do not use damaged nozzles.
5. The head gasket is seldom a source of leaks. Do not use gasket
cement. If the head gasket must be replaced, order a replacement
from the Sedimentation Project. Use of a gasket having improper
thickness will cause misalignment between the nozzle nut and valve
body.
6. Never submerge a sampler beyond its rated depth (180 feet with
pint container or 120 feet with quart container).
A copy of the Instructions for US P-61-Al Suspended Sediment
Sampler is attached. All operators using point-integrating
samplers should be entirely familiar with these instructions.
R. J. Pickering
Enclosure
WRD Distribution: A, FO
FEDERAL INTER-AGENCY SEDIMENTATION PROJECT
St Anthony Falls Hydraulic Laboratory
Hennepin Island & Third Ave S E.
Minneapolis, Minnesota 55414
INSTRUCTIONS FOR US P-61-Al
SUSPENDED SEDIMENT SAMPLER
These instructions describe the sampler, present detailed
maintenance procedures, and outline general operating techniques
They are not intended as a comprehensive field guide For details
that pertain to sampling theory and sample analysis, refer to
Report No 14(1), Techniques of Water-Resources Investigations of
the U S. Geological Survey(2), and the ASCE Sedimentation
Engineering Manual(3).
Purpose
The US P-61-Al was designed to collect special samples required to
determine the suspended-sediment discharge of a river or stream.
The sampler may be used to collect either depth-integrated samples
or point-integrated samples. Before shipment each sampler is
checked and, if necessary, adjusted to sample at, or very near,
stream velocity. To maintain the adjustment and thereby insure
samples of high quality, operators are urged to review and follow
these instructions.
Physical Characteristics
The sampler is cast of bronze, weighs 105 pounds, has an overall
length of 28 inches and an overall height slightly less than 13
inches (fig 1). It will hold either a quart (Owens ~ Illinois
#6762) or pint (round glass milk bottle) sample container The
sampler consists of two major parts; the head and the body. The
head supports both the sampling nozzle and the electrically-
operated, two-position rotary valve Also, it contains several
passageways that convey air and water The body supports the sample
container, and the tail vanes which align the nozzle with the
approaching stream flow The body has a hollow interior which
serves as a compression chamber that forces air into both the head
cavity and the sample container. A latch and hinge hold the head
and body together. The head pivots on the hinge and swings away
from the mouth of the sample container
Valve Mechanism
The valve serves two purposes: it starts and stops both liquid
flow into the sample container and air flow to and from the
container. The porting diagram for the valve is shown in fig 2
With no electrical power applied, the valve is in the pressure
equalizing position As the sampler is lowered through the water,
hydrostatic pressure forces-water through the holes in the belly
of the sampler and then into the compression chamber Air inside
the chamber flows through the tube that leads to the head cavity
At the head-body junction, the air flows through the air line
gasket (part 29, fig 1) Air in the head-cavity flows through the
valve plug (fig 2, section B-B, pressure equalizing position) and
into the sample container The air flow balances the pressure
inside the sample bottle with that near the nozzle. ~hen power is
applied, the solenoid turns the valve into the sampling position,
fig 2. The connection to the compression chamber closes and the
passage leading from the nozzle to the sample container opens.
Without surging, the sample flows into the sample container
Leading from the sample container to the ambient flow, another
passage steadily expels air displaced by the sample Sampling
terminates when power is removed and the valve plug returns to the
equalizing position
Power Supply
To support the sampler and to transmit power, the sampler must be
suspended on a sheathed single-conductor cable To minimize drag,
the cable should have a diameter of 1/8" or smaller. To minimize
power supply voltage, the resistance should not exceed 100 ohms
per 1000 feet An Ellsworth cable is commonly used and may be
purchased from the U S Geological Survey, Shipping and Receiving
Section, Mail Stop 231, Reston, Virginia 22092. Connect the
sheath, exterior load-bearing strands, to a special clamp and pin
the clamp to the top end of the hangar bar. Connect the insulated
conductor, located in the center of the cable, to the insulated
wire on the left side of the head. This completes connections at
the sampler end of the cable On the reel end, secure the cable to
the reel then connect the center conductor ~o the slip-ring. When
power is applied at the reel, current will flow from the supply,
through the center conductor and then through the solenoid Current
will return through the sampler body, the hangar bar, the cable
sheath, and the reel frame
The power supply must be direct-current which, at remote sites, is
most conveniently obtained from dry or wet cell batteries The
supply voltage is set by the required current and the total
resistance in the cable and solenoid. For a 100 foot cable with a
resistance of 100 ohms/1000 feet, the cable resistance will be 10
ohms. The rotary solenoid has a resistance of 24 ohms and will
require one ampere to rotate the valve With this cable, the
voltage must be no less than 36 volts To provide for a margin of
reliability and for battery discharge, a 48 volt d c supply is
recommended. Eight 6-volt "hot shot" batteries or from eight to
ten 6-volt lantern batteries can be used Other batteries such as
wet cells can be used, but any battery selected must have capacity
sufficient to sustain the required voltage while delivering a
current of one ampere. A special capactive-discharge supply (BP-
76) may be purchased from the Sedimentation Project. Compared to
batteries, the unit is lighter and smaller but is more expensive.
Accessories
For field sampling with the P-61, a cable, power supply, switch,
crane, reel, cable connector, hangar bar, and hangar bar pin are
required. Most of these items can be obtained from the Geological
Survey at Reston, Virginia A standard threaded hangar bar pin is
recommended but a plain 3/8" x 3" diameter steel pin may be
substituted. If a plain pin is used the hangar bar must have a
smooth hole rather than a threaded hole. The set screw, (P61-25,
fig. 1) must be installed to retain the pin. With a battery supply
a single-pole single-throw toggle switch will be required This
type of switch is available at local hardware or electronic
stores. Six to ten feet of 14 AWG stranded, insulated wire and two
clips will be needed to connect the batteries to the reel. The BP-
76 includes a switch and wire.
Operation
Fasten one end of the cable to the reel and connect the center
conductor to the reel slip-ring. ~eel the cable onto the drum,
mount the reel on the crane, then thread the cable over the crane
sheaves. Clamp the other end of the cable into the cable-
connector, then suspend the sampler on the hangar bar. Connect the
center conductor to the sampler lead wire. On the power supply
connect one wire to the reel slip-ring and connect the other wire
to the frame of the crane or reel. The P-61 solenoid is not
sensitive to direction of current so connections can be made
without regard for polarity. Check for rotation of the valve plug
by operating the switch several times while sighting through the
nozzle. If the sampler has been in storage, water-formed deposits
may cause the valve plug to seize in the valve plug body. If the
valve will not turn, connect the power supply directly to the
sampler leat-wire, apply power, and strike the side of the sampler
head with a rubber or wood mallet. Never strike the nozzle. If a
few sharp blows will not free the valve, refer to the Maintenance
Section When the valve is operating properly, insert a sample
bottle then close the head slowly. Guide the lip of the bottle so
that it centers and seals against the face of the bottle gasket.
Insert the aluminum adapter into the sample-container cavity if
pint bottles are to be used Lower the sampler to the desired
depth, then close the switch for the desired sampling interval.
Open the switch, hoist the sampler, ant remove the sample bottle
Optimum sampling intervals vary
with stream velocity and container size, so some experimentation
will be necessary The interval must be chosen so that the
container is approximately 2/3 full Samples that are overfilled
must be discarded and the process repeated with a shorter interval
To be valid, a sample must enter the container only through the
nozzle with a pint container the bronze P-61-Al sampler will
function properly to a depth of 180 feet but with a quart
container, the depth is only 120 feet At greater depths,water
instead of air, will flow from the compression chamber and enter
the sample container
To collect a point-integrated sample, support the P-61 at a fixed
depth during the entire sampling interval To collect a depth-
integrated sample first open the valve then depending upon depth
and velocity, either raise or lower the sampler at a uniform rate.
If the stream is less than 18 feet deep and the velocity is
moderate, close the switch to open the valve then lower the
sampler at a uniform rate from the water surface to the bottom of
the stream When the sampler touches bottom, instantly reverse reel
rotation and,at a uniform rate, hoist the sampler through the
flow. Switch the power off only after the sampler emerges from the
stream If the stream is between 18 and 30 feet deep, or has a high
velocity, the sampler may be used to depth-integrate in one
direction, from the bottom of the stream to the surface With power
off, lower the sampler to the stream bed. Apply power then, at the
same instant, start hoisting at a uniform rate Switch power off
when the nozzle breaks through the surface
Deep, fast streams may be depth-integrated in sections At each
sampling station, divide the vertical into several segments, then
depth-integrate each segment individually When depth-integrating,
never lower or hoist the sampler at a rate that exceeds 0 4 of the
mean stream velocity For shallow streams transit rates are less
Report No 14, p. 45 shows rate limits imposed by each of several
factors Refer to the diagram for the 3/16" nozzle With the quart
container, maximum rates as limited by air compression must be
reduced to 1/2 of those shown in Report No 14(4). When handling a
P-61 filled with a sample, never allow the nose to tilt down more
than ten degrees. A portion of the sample may escape through the
tube leading to the compression chamber
Those unfamiliar with sampling theory or program objectives, must
consult with the hydrologist to clarify details such as the number
and the location of sampling stations within a particular cross
section
Maintenance
If the valve plug fails to turn, disassemble the head. Remove the
nozzle, then remove the hinge pin to free the head from the body
To free the head the catch may be left in place, however, if the
catch mechanism is to be disassembled take precaution to restrain
the spring under the catch With the head free of the body, remove
the six cap-screws that hold the head-base to the head-cover
Separate the two parts and avoid damage to the gasket
To disassemble the valve mechanism, first remove the screw in the
end of the valve plug, then remove the washer, spring, and spring
boss Note the shape of the valve arm and its orientation Punch
marks on the valve plug and valve arm show their correct alignment
The solenoid must be removed to free the plug from the valve body
On the band that holds the solenoid, loosen the set-screw and
remove the exposed screw that anchors the band. Note the
orientation of the solenoid leads, then slide the solenoid free of
the band Now slide the valve plug out of the valve body Use fine
steel wool or fine sandpaper to clean and polish the plug and the
inside of the valve body Household cleansers should not be used
because the abrasive may become imbedded in the brass valve body
and cause the plug to bind To check the solenoid, apply voltage
directly to the solenoid lead wires. When power is applied, the
solenoid should rotate 45! then, when power is removed, the
solenoid spring should return the armature to its rest position If
the solenoid fails to turn, corrosion may have damaged the winding
or ball-race Replace the complete solenoid.
To reassemble, reverse the above procedure The clock-type spring
should be wound approximately 1/2 revolution and mounted so that
movement of the valve to the sampling position tightens the
spring. After all parts are assembled energize the solenoid. The
valve arm should seat tightly against the stop and the valve plug
sampling-intake hole should align with the corresponding hole
through the valve body. If necessary, adjust the solenoid so that
it does not bind against the valve wheel Clean the surface of the
head gasket, position the head cover, then insert the six cap
screws. Seat the screws firmly but do not tighten Face the screw
heads and rotate the head so that the catch is at the 12 o'clock
position. At the two o'clock position, label the screw number 1 In
a clockwise direction label each screw then tighten in the
sequence 1-4-6-3-5-2 Repeat the tightening sequence two or three
times, each time increase the torque. Final torque should be 100-
125 pound inches. The exact torque is not critical but all screws
should be tightened as nearly equal as "feel" permits
Corrosive damage to the plug and solenoid assembly is caused by
water that collects in the head cavity Even a small quantity will
cause problems if the sampler is stored before removing the water
When sampling is complete, remove the head base Drain and, with a
cloth, dry ~he interior of the head cover then let the assembly
air-dry before reinstalling the base. Slow leaks around the valve
plug are unavoidable because the plug must be loose enough to
rotate freely Parts that are missing or defective will cause
serious leaks. A missing or defective nozzle gasket (o-ring) will
allow water to leak into the head A worn or missing air-line
gasket will allow water to enter the head and will interfere with
the compression process. To seal, the air-line gasket must be
pliable To check for seal, open the head, place a paper strip
against the body where the gasket makes contact, then close the
head If the paper is loose or can be withdrawn easily, replace the
gasket. Contrary to expectations, the head gasket is seldom a
source of leaks. Do not use gasket cement If the head gasket must
be replaced, order a replacement from the project. In emergencies,
gaskets may be cut locally, but be sure to use gasket stock of the
same thickness as the original. Improper gasket thickness will
cause misalignment between the nozzle ~and valve body. Even with
good seals, improper operation can cause damage. If the sampler is
submerged to depths beyond its rating or if the sampler is
submerged without a proper sample container, the compression
chamber will fill and water will enter the head through the
compression line.
A nozzle that is bent or burred around the ends will contribute to
sampling errors and must be replaced. Replacement parts may be
ordered from the Federal Inter-Agency Sedimentation Project. Also,
samplers that require maintenance or recalibration may be shipped
to the project.
(l) Inter-Agency Committee on Water Resources, "Determination of
fluvial sediment discharge," Rept 14, A study of methods used in
measurement and analysis of sediment loads in streams;
Subcommittee on Sedimentation, Minneapolis, Minnesota, 1963.
(2) Guy, H. P.; Laboratory theory and methods for sediment
analysis, Techniques of water-resources investigations of the U.
S. Geological Survey, bk 5, ch Cl, 1969.
(3) American Society of Civil Engineers, "Sedimentation
Engineering," by Task Committee, V. A Vanoni, ed , ASCE, New York,
N. Y., 1975.
(4) Inter-Agency Committee on Water Resources, "The design of
improved types of suspended sediment samplers," Rept. 6, A study
of methods used in measurement and analysis of sediment loads in
streams; Subcommittee on Sedimentation, Minneapolis, Minnesota,
1952, p 22-34