WEBTEC DHT 2 Series User manual

Digital Hydraulic Testers
DHT Series 2
DHCR Series 2
Webtec Products Limited
Digital Hydraulic Testers Operating Manual
www.webtec.co.uk

1
Introduction
DH Series Digital Portable Hydraulic Testers have been designed for easy connection to a
hydraulic circuit so that flow, pressure and temperature can be readily checked. To facilitate
easy operation all common engineering units can be selected and the display update time can
be varied. Testers can take full back pressure up to 350/420 bar (depending on model) and the
built-in loading valve enables many of the operating conditions to be simulated. The tester can
be connected anywhere in the hydraulic system to test pumps motors, valves and cylinders in
both flow directions.
Bi-Directional Flow Testing
1. The loading valve gives smooth control of pressure in both flow directions and is protected
in both flow directions by two replaceable safety discs which are designed to rupture at
approximately 7 bar (100 psi) over the maximum working pressure. When these discs
rupture the oil by-passes the loading valve at low pressure and continues to flow freely
through the hydraulic system. A range of pressure safety discs are available to protect both
the tester and other components in the hydraulic system.
2. Although the bi-directional tester can be used in both flow directions, the preferred direction
is indicated by IN and OUT on the tester block. When the tester block is used for reverse
flow tests, slightly lower accuracies may be obtained depending on the oil viscosity, density
and compressibility.
3. The tester should be connected to the hydraulic circuit by means of flexible hoses, DHT
1 - 2 metre long and DHCR 1/4 metre long. The use of quick-disconnect couplings can save
time. Make sure the hoses are long enough so that the tester can be used conveniently on
the machine. The hoses and fittings at the inlet to the tester must be of adequate size for
the flow being tested. Elbows, rotary couplings etc., at the inlet and outlet ports of the tester
should be avoided to ensure accurate readings.
4. With the DHCR Testers connect the cable and micro-bore hose assembly at the readout
then connect to the flow block. IMPORTANT, after testing, disconnect at the flow block first
to avoid oil spillage.
5. On the DHT Testers the use of the flexible hoses will help to isolate the test unit from
vibration which often exists, DHCR Testers may be connected with rigid pipes.
6. After installing the Tester it is important to ensure that all connections are tightened and the
oil can flow freely throughout the hydraulic system BEFORE running the machine at full
speed. Check that the circuit is correctly connected and any shut-offvalves are opened,
also quick disconnect couplers MUST be open. IMPORTANT start the pump momentarily
to ensure there is no obstruction which could cause pressure build up.
7. When using the DHCR or an external flow block with the DHT Testers ensure that the
appropriate calibration factor is entered. See section on PROGRAMMING for details.
8. Testers have an automatic electronic system which shuts the power off after approximately
15 minutes should you forget. To reactivate the tester, press the “ON” KEY.

9. If using the LT5, LT10 or LT20 positive displacement flow blocks as remote input to
measure case drain leakage, it is recommended that a relief valve or check valve 1 bar (15
psi) is fitted in a tee to protect the pump or motor against excessive pressure in the event
of a surge flow. Consult Sales Office for further information on Tee fittings.
10. An additional gauge may be connected to the tester block using a pressure test point and
micro bore hose. See page 4 for details. Note: Always disconnect the low pressure gauge
for high pressure testing if it is not protected by an automatic cut-out valve.
Trouble Shooting with the Hydraulic Tester
PRELIMINARY: Check oil level in tank, pump drive, valve linkage for damaged parts, external
oil leaks etc
2
Excessive pump noise
fluctuating pressure
Low flow under no load
Decreasing performance
as pressure increases on
all circuits
On one circuit
Fails to hold load
Pump cavitation caused by:
a) Clogged suction filter
b) Restricted suction line
c) Air leak in pump suction line,
fittings, shaft seals etc.
d) Pump speed too high
Internal leakage in:
a) Pump
b) Main Relief Valve
c) Directional Control Valve
d) Cylinder or Hydraulic Motor
Directional Control Valve
Cross line Relief Valve
Cylinder
3.0; 4.1
3.0; 4.1
4.2; 4.3
4.2; 4.3; 4.4; 5.0
5.1; 5.2
4.2; 4.3; 4.4; 5.0
5.02
5.0; 5.2
Do not use with Water
The standard Webtec Hydraulic Testers are designed for use with mineral oil having reasonable
lubrication properties. They are not suitable for use with water or fluids with a high water
content. If a tester is used with water it should be flushed immediately after use with white or
methylated spirit or similar and then flushed with mineral oil to minimise any internal corrosion.
This may avoid an expensive repair. Damage to a tester from the use of a non-approved fluid
invalidates our normal warranty.
Problem Possible Cause Suggested Test,
See Paragraph:

3
Operation
Models: DHT and DHCR
Temperature
The thermistor type temperature transducer is in contact with the oil flow and temperature is
displayed on the left hand side of the digital display. Temperature from the internal transducer
is displayed in the INT and TACH position; temperature from a remote turbine is displayed in
the EXT position. Pressing the °C/°F button toggles the display between Centigrade and
Fahrenheit, the unit selected is indicated by a cursor arrow.
Flow Meter
The Flow Meter comprises an axial turbine mounted in an aluminium block. The oil flow rotates
the turbine and its speed is proportional to the oil velocity. The revolutions of the turbine are
measured by means of a magnetic sensing head which feeds a pulse every time a turbine blade
goes by,to an electric circuit. The circuit amplifies the pulse, shapes it into square wave form
and has a digital output which is directly proportional to the number of pulses per second.
Flowrate is displayed in the right hand side of the digital display when INT or EXT are selected.
Pressing the units button switches the display to USGPM, IGPM or LPM and the selection is
indicated by a cursor arrow. When the flow rate falls below the minimum allowable “L” is
indicated on the display. When flowrate exceeds the maximum “H” is indicated on the display.
Tachometer
RPM is displayed in the right hand side of the digital display when “TACH” is selected on the
rotary switch. Pressing the units button switches to RPM or RPM/N indication. RPM assumes
the sensor provides one pulse per revolution of the shaft. RPM/N assumes the sensor provides
Npulses each revolution of the shaft. (See section on Tacho Generator) The value of N can be
varied (See section on programming).
Pressure Gauge
The pressure gauge has a spiral Bourdon tube and the gauge case is filled with glycerine to
ensure good dampening on pulsating pressures. The gauge is connected to the turbine block
by fine bore capillary tube. Testers with BUILT-IN load valve have a shuttle valve which
automatically reads the highest pressure in both directions of flow. A gauge port is provided in
the block for the addition of a low pressure gauge.
Fast Button
The fast button changes the update time of the display. In some situations quick response to
flowrate changes is required. With the cursor arrow highlighting the fast position, the update
time is approximately 1/3 second. Otherwise the update time is approximately 1 second. When
using the fast update, the display will be less stable on flow and shaft speed.

4
Tach. Ext. Flow
Off
Tach.
Int. Flow
Ext. Flow
-
9V
+
!
-)-
Int. Flow
Fast OnUnits°C/°F
FLOW / RPM
TEMPERATURE
o
F
o
C
US
GPM
IMP
GPM
RPM
NRPM LPMFAST
ON Button
The unit is designed to turn off automatically after approximately 15 minutes to conserve power.
When this occurs user programmed values are retained in the memory. The unit is restarted by
pressing the “ON” button.
Bi-Directional Loading Valve
The reverse flow valve gives positive shut-off and pressure control in both directions of flow.
The loading valve has two easily replaceable safety discs located in the valve assembly which
internally protect the tester and machine in both flow directions.
Accessories
An infrared photo-tachometer is available along with a flexible magnetic base.
Low Pressure Gauge Kit comprises 63 mm 2 1/2” Glycerine filled 40 bar (600 psi) gauge with
automatic cut-out valve, pressure test point and 300 mm (12”) long micro bore hose. The test
point is fitted permanently into the tester block and the low pressure gauge can be connected
by hand without the need to stop the machine.
Adaptors.Fitting kits are available for all testers. Consult Sales Office.

5
Programming
Models DHT and DHCR
The DHT and specified DHCR Testers are pre-programmed with the calibration number (PPL)
as follows: INTERNAL meter factor to suit the tester turbine, EXTERNAL meter has a standard
calibration number and the actual calibration number from the turbine must be loaded into the
unit.
The DHCR unspecified Testers INTERNAL and EXTERNAL inputs, the calibration numbers
have not been loaded. Both inputs have the standard calibration numbers.
To program these values follow the procedure below:
PROGRAM MODE - EXT, INT and TACH.
External Flow - EXT
1.) Turn selector switch to Ext.Flow and press the ON button.
2.) Press °C/°F button and hold down. Then press ON i.e. two buttons are pressed at the
same time.
3.) On the left side of the display appears the turbine type number i.e. 750 is 750 lpm, on
the right side of the display is the standard calibration number. Use the FAST key to
browse through the list of turbine types. Press UNITS to select a turbine type.
4.) Use the FAST key to increment the number above the cursor. Press UNITS to move to
the next column. After entering the calibration factor press UNITS until the display
overflows. The display will now show the number of digits after the decimal point. Use
the FAST key to select the number of decimal places to appear on the display.
5.) Press the ON button to store the entries.
Internal Flow - INT
The calibration factor for internal flow on the DHT Testers is pre-programmed. It can be checked
as detailed above, but it is not possible to change it. The internal calibration factor on the DHCR
should be loaded by switching to INT and repeating the program instructions above.
TACH
The calibration factor for RPM is pre-programmed for a factor of 1.0. For the RPM/N function
the tachometer provides N pulses per revolution of the shaft.
To set factor N:
1.) Turn selector switch to TACH and press the ON button.
2.) Press °C/°F button and hold down. Then press ON i.e. two buttons are pressed at the
same time.
3.) The display shows the current value for “N”. Use the FAST key to increment the number
above the cursor. Press UNITS to move to the next column.
4.) Press the ON button to store the entries.

6
Instructions for using the portable Hydraulic Tester
Models - DHT and DHCR
0.0 The Tester is designed to measure flow, pressure, temperature and rpm. It can take full
system pressure up to 420 bar (depending on model) and measure flow in both directions
for motor and cylinder testing.
0.1 Make all tests at operating temperatures because as the oil temperature increases it
becomes thinner and any internal leakage becomes greater.
0.2 Testing will be easier and faster if quick disconnect couplers are used to attach the Test Unit.
0.3 There are two basic test ‘set-ups’ when using either the DHT or DHCR Testers:
A) The In Line test to check out pumps, entire systems and also monitoring operating
conditions.
B) The Tee Test to check out pumps, directional control valves and overall system
condition.
0.4 A preliminary check of the hydraulic system’s oil supply, pump rotation, filters, oil lines,
cylinder rods as well as looking for external leaks should be made prior to installing the
hydraulic tester.
1.0 Installing the Test Unit
1.1 Connect the Tester to the circuit, see page 22 for Port Sizes. The inlet and outlet ports
are marked on the turbine block. Use hoses and fittings of sufficient diameter for the flow
being tested. Avoid restrictions at inlet and outlet ports of the Tester. Also avoid sharp
bends because at high pressure hoses will deflect and straighten under pressure.
1.2 When the pressure loading valve is used ensure it is fully opened by turning the knob
counter clockwise.
1.3 When no flow is passing through the turbine, the display will read “L” for “LOW” flow.
1.4 When low pressure testing is required connect the optional low pressure gauge with
quick disconnect coupler only after the pressure has first been checked on the high
pressure gauge. REMEMBER to disconnect the low pressure gauge for high pressure
tests otherwise the gauge will be damaged. Note: An automatic cut-out valve which
protects the LP gauge is available. Consult sales office.
1.5 With the DHCR Testers connect the cable and micro-bore hose assembly at the
readout then connect to the flow block. IMPORTANT after testing disconnect at the
flow block first to avoid oil spillage.
1.6 Connect the remote flow block to the circuit as specified above in 1.1 and 1.2.
1.7 Select “EXT” on switch and program in correct meter factor if not already present.
(see section on programming).
1.8 Continue tests as specified for the hydraulic tester.

2.0 Standard Test Conditions
2.1 Position the Hydraulic Test Unit as described in paragraph 3.0 or 4.0.
2.2 Open loading valve. (Rotate counter-clockwise) and select high flow range.
2.3 Start pump momentarily to ensure that oil flows freely through the hydraulic system,
then run pump at normal maximum speed. Do not change pump speed while using
the loading valve.
2.4 Slowly close Test Unit Loading Valve to develop desired pressure. Run the machine
until normal operating temperature is reached.
2.5 Open the Testing Loading Valve and proceed with required test procedure (see
paragraph 3.0 or 4.0).
2.6 Keep a record of flow readings at various operating pressures for comparison of test
results. The machine Manufacturer’s service manual should be consulted.
3.0 Test 1 - Pump In Line Test (See Test Diagram A1) using DHT or DHCR
3.1 Install the Tester into the system between the pump outlet port and the inlet to the
directional control valve.
3.2 Open Tester loading valve to read maximum pump flow at minimum pressure.
3.3 Close loading valve slowly to increase pressure and note reduction of flow as the
pressure is increased to maximum pump pressure to determine pump condition.
7
Drawing A1
Directional Valve
Cylinder
Remote
Flow Block
Pump DHT Test Hose
Relief
Valve
US

3.4 Pump flow at rated pressure can now be checked against the pump manufacturer’s
specifications. The decrease in flow from the minimum pressure to maximum
pressure determines the pump condition. Typically a worn or damaged pump will lose
20 - 30 percent. A pump that delivers low flow at both minimum and maximum
pressure indicates suction problems. Blocked suction filters and pump cavitation
problems can also be checked by recording the pump flow at various engine speeds.
3.5 The tester can be used at several points in the circuit and the machine can be used
under its normal working conditions to evaluate the performance of the circuit
elements, such as pump, control valve, cylinder and hydraulic motor.
4.0 Test B - ‘TEE’ Test (See Drawing A2) using DHT or DHCR
4.1 A ‘Tee’ must be installed at one point between the pump and control valve then
connected to the “IN” port of the Tester.The “OUT” port of the tester is connected
back to the tank. Make sure the loading valve is open. Note: Typically an elbow may
be changed to a ‘Tee’ in most hydraulic circuits and the ‘Tee’ can be capped with a
steel cap when not used for testing.
4.12 Pump Test. Disconnect and plug connection to control valve and proceed as in
paragraph 3.2; 3.3 and 3.4.
4.2 Overall System and Relief Valve Test (See drawing A2)
(For relief valve integral with directional control valves)
4.21 Connect control valve to ‘Tee’. Operate control valve to extend the cylinder to
end of stroke.
4.22 Close the Tester loading valve while watching pressure and flow meter reading.
Pressure will increase until relief valve opens at which point flow reading will
return to zero. Note or record pressure at this point. Adjust the relief valve if the
pressure is below the recommended setting.
8
Drawing A2
Cylinder
Pump Tee Connection
Test Hose
Relief Valve
Overall System
‘Tee’ Test
DHT
US

Pump
Relief
Valve
Flow Block
&Load Valve
Test Hose Relief
Valve
Directional Valve
Motor
Remote
Flow
Block
DHCR
Readout
It is not unusual for a relief valve to start cracking open below the maximum
pressure setting causing considerable leakage and loss of machine
performance. The cracking pressure can be checked by increasing the
pressure slowly and noting the pressure at which the flow starts falling rapidly
to zero. The maximum relief valve setting is when the flow is at zero.
4.3 Control Valve. Cylinder ‘TEE’ Test
4.31 Put control valve in power position. (On multiple spool valves, only one spool
should be in a power position at any one time). The cylinder should be
extended to the end of the stroke.
4.32 Close tester loading valve slowly while recording pressures and flow rate.
4.33 Repeat 4.32 for power position, for all spools of all control valves.
4.331 If all components are in good operating condition, pressure and flow
measurements should be the same as in the pump test paragraph 3.0.
4.332 If the decrease in the flow of any control valve position is noted, leakage is
indicated in this control valve or cylinder. See paragraph 4.4 for test routine
to determine which is at fault.
4.333 If the decrease in flow is the same for the control valve(s) in all positions,
it indicates the relief valve is at fault. (Note: This can also indicate some
other leak is present in the control valve such as defective casting - but
always check the relief valve FIRST)
4.4 Additional test to locate fault in control valve or cylinder (see paragraph 4.332).
Disconnect line to cylinder and plug valve port.
4.41 Place control valve handle in position where greatest decrease of flow was
noted.
4.42 Close tester loading valve and record both pressure and flow.
4.43 If the SAME decrease in flow is noted as in test per paragraph 4.332 then the
control valve is at fault. HOWEVER, if the flow readings are now higher and
comparable to the other control valves, then a faulty cylinder is indicated.
9
Drawing B1

10
5.0 Directional Control Valve ‘In-Line’ Test (See drawing B.1) using DHT or DHCR
5.01 To check the relief valve pressure setting where relief valves are integral with control
valve, install flow meter in the cylinder line as shown in drawing B1,ensuring that
loading valve is open (turn anti-clockwise). Start pump and operate the lever on the
valve in which the tester is situated to raise load. Slowly close the loading valve (turn
clockwise), reading pressure and flow, continue until loading valve is fully closed,
pressure reading obtained is then relief valve pressure. Compare with manufacturer’s
recommendations. Adjust relief valve if necessary. Using bi-directional flow testers,
the cylinder and valve may be tested in the opposite direction by operating the lever
to retract the cylinder.
5.02 Control Valve Leakage
With flow meter installed as in 5.01, repeat test and compare flow readings obtained
for comparable pump test 3.3. Differences in flow readings indicate leakage within
control valve. Repeat test for all power ports to fully determine valve condition.
Replace control valve block or valve segment where necessary.
5.1 Cylinder Test (See Drawing B.1)
5.11 If the cylinder is slow in operation or cylinder ‘creeps’ under load the following
test should be carried out to check the cylinder seals.
Install the flow meter ‘in-line’ as shown in Drawing B.1. Actuate cylinder to raise
and lower the load. Note flow and pressure readings, also note the time taken
by the cylinder to reach full stroke. Compare all readings with manufacturer’s
recommended figures. If flow is correct but time to extend cylinder is greater
than expected leakage across the cylinder seals is indicated. If flow is lower
than expected, investigate control valve function. See Test 5.0.
5.2 Motor Test
5.21 Motor performance is checked by measuring the flow and comparing it to the
equivalent motor speed. Install the tester or remote flow block in the line
upstream of the motor as indicated in the drawing B.1. Fully open the loading
valve and operate the directional control valve ensuring the motor rotates in the
correct direction. Allow motor to run under normal load. Note flow and pressure
readings. If flow is below manufacturer’s data sheet or lower than pump test
(3.0) investigate control valve function. See Test (5.0).
Note: The motor may only be tested in reverse if it has an external drain. Do
not pressurise the outlet port of the motor without first checking the allowable
back pressure with the manufacturer.
Motor Leakage
5.22 Measure hydraulic motor r.p.m. with tachometer when motor is working at
normal pressure. If the motor speed is low and the inlet flow in 5.21 is found to
be correct, internal leakage in the motor is indicated. Check the motor leakage
by installing the remote flow block in the motor case drain. Note: most motors
not fitted with high pressure shaft seals have a maximum case drain pressure
of 1 bar (15 psi)
5.23 When the motor does not have an external drain or the motor cannot be back
pressure loaded connect tester in the other line and repeat the test 5.21 and
5.22 for the other motor direction.

Pump
Cylinder
Motor
Directional Valve
Relief
Valve
Test Hose
Relief Valve
11
Drawing B2
5.3 Alternative Cylinder and Motor Test
5.31 Both motors and cylinders may also be tested as shown in drawing B.2.
Disconnect the two lines from the motor and connect the tester into these lines.
Fully open the loading valve, start the pump and bias the directional valve to
allow flow to the inlet port of the tester. Slowly close the loading valve by turning
clockwise and note the flow and pressure. If the flow is below the
manufacturer’s data or lower than the pump flow test (3.0) investigate the
control valve function. See Test (5.0). If the flow is correct and the speed is slow
this indicates a defective motor or cylinder.
Operate the directional valve to reverse the flow through the tester and record
the flow throughout the pressure range.

12
Photo Tachometer
6.0 General Description
The photo tachometer consists of the coaxial photo tach head, reflective tape and built-in
connecting cable.
RPM is displayed in the right hand side of the digital display when TACH is selected on the
rotary switch. Pressing the units button switches to RPM or RPM/N. RPM assumes the
sensor provides one pulse per revolution of the shaft. RPM/N assumes the sensor provides
Npulses per revolution of the shaft. The value of N can be varied (See section on
programming) the tester.
6.1 Photo Tach Head
The Photo Tach Head senses the speed of a rotating body without physical contact.
Its design permits it to be used over a wide range of distances from the rotating body.
When reflected light is detected by the photo tachometer a red ‘on target’ LED
indicator illuminates to confirm alignment. Accessories include a flex arm and
magnetic base. These can be used in various combinations to mount the Photo Tach
Head. The Unit has a built-in cable to connect the tach head to the tester.
7.0 Object Preparation
The Photo Tach Head will only sense the change in reflected light from a moving object.
Therefore, a rotating shaft with a uniform reflective surface must be marked with pieces of
reflective tape supplied with the photo-tachometer. Select a convenient position on the
shaft, pulley or coupling which has a minimum diameter of 35 mm (1.4 inches). Larger
diameter shafts will give better results, particularly at high speeds. The surface should be
preferably free from bolt holes, keyways etc. Clean the surface and fix a piece of reflective
tape, approximately 20 mm (0.8 inches) long. If this does not give sufficient contrast it may
be necessary to paint or cover the remainder of the shaft with matt black or use larger
pieces of reflective tape.
For shaft speeds lower than 800 rpm use 2 pieces of reflective tape, and program the
“TACH” channel with a factor of 2.
7.1 Obtaining a Reading
Connect the cable in the Tach Head and attach the magnetic base. Fix the magnetic
base in a suitable position and aim the light at the rotating object. Switch on the tester,
select TACH and position the Photo Tach Head 150 mm (6 inches) away from the
object and read the r.p.m. directly on the meter. If no reading is obtained move the
head closer to the shaft. If the reading is fluctuating select slow update and increase
the distance from the shaft until a steady reading is obtained. The distance of the
Photo Tach Head from the object will vary depending on the ambient lighting, size of
the object, amount of contrast and the speed of the object. Certain types of ambient
lighting may require shading of the rotating object or applying a larger reflective mark
will correct the situation.
Note: Infrared light is NOT visible to the naked eye.

Service Instructions
If the tester does not indicate flow:
Flowmeter
A) Turn the selector switch to “INT”. If the digital display is absent press the “ON” button. If
the display is still faint or absent check the condition of the battery and battery connections
located in the front panel of the DHT and in the side of the DHCR case. Replace battery if
necessary.
B) If the flowmeter displays a valid temperature but no flow when in “INT” position it is likely
that the turbine has become jammed by debris. This usually consists of pieces of ‘O’ ring,
PTFE tape etc. Remove and clean turbine as in section D.
C) If the flowmeter does not display flow when a remote flow block is connected, first ensure
that the unit is programmed with a Meter Factor (See programming section). Then check
all cable connections and finally the operation of the remote turbine as in section D.
D) Turbine
To remove turbine assembly for cleaning, remove locking ring from inlet port, Fig. 1 hold
turbine flow straighteners with soft nose pliers and pull gently. Fig. 2 DO NOT ROTATE.
Remove debris and wash in clean organic solvent. Turbine should revolve freely when
blown along flow straightener.
E) Ensure the turbine block is also free of debris. Replace the turbine assembly ensuring the
clipped corner of the flow straightener is returned to the 1 o’clock position.
F) The turbine can be driven with an air flow to check the flowmeter.For this test if a loading
valve is fitted it should be opened completely.Direct the air flow through the inlet port of
the turbine, switch on the tester to “INT”. The air should rotate the turbine and the digital
display indicate the flow. If there is no reading check that the turbine is rotating. When
using compressed air,do not overspeed the turbine or the meter will be overloaded.
G) Cable/Hose Connections on the DHCR. Ensure that the cable and plugs are in good
condition and free from cuts. It is important that the connections on the flow block and
readout are correctly made. Note: ALWAYS disconnect the hose from flow block first or
oil leakage will occur. Ensure the plug on the flow block is correctly connected.
WARNING: Care should be taken while removing the turbine assembly. Damage to the
bearing will cause a loss of accuracy and the tester could malfunction.
For recalibration contact Webtec Products Ltd or your local sales office.
13
Fig. 1 Fig. 2

14
Loading Valve
DHCR Testers up to 125 lpm 30 gpm with HV100 Loading Valve
If the handle becomes difficult to turn under pressure or will not close, remove the handle
assembly with a 7/8“ AF spanner. Check for worn valve spindle and seat, damaged seals or
contamination. Note: If the pressure does not increase progressively when the loading valve is
operated, check if the safety discs have ruptured.
The loading valve (Fig. 3) is fitted with two safety discs which are designed to rupture internally
at approximately 7 bar (100psi) over the maximum pressure. When these discs fail the loading
valve becomes inoperative and the oil flows freely downstream. To replace the discs, remove
the cartridge assembly by unscrewing the 1 3/8“ AF hexagon. Unscrew internal holder in
cartridge, remove the two ruptured safety discs and fit new discs, as supplied, one each side
of the spacing ring (Fig. 4). Tighten internal disc holder to 40 lb.ft. (54 Nm). Replace the
cartridge in the valve body. Do not fit discs of unapproved design or material.
Replacement Safety Discs for all Models
Replacement safety discs available to the following specification: Blue 345 bar,(5000 psi), Red
420 bar (6000 psi). Consult Sales Office for lower pressure ratings. State the Tester model
number when ordering replacements.
Fig. 3
Fig. 4
Spacer
Disc
Disc holder
Safety Disc Cartridge
Disc

Loading Valve
DHT & DHCR Testers 300 & 400 lpm Models
If the loading valve becomes difficult to turn under pressure or will not close, remove the 4
socket screws. Check for worn valve seat, damaged or leaking seals and contamination. Note:
If the pressure does not increase progressively when the loading valve is operated, check if the
safety discs have been ruptured. Assemble the loading valve into the flow block ensuring that
the guide pin is located in the slot on the poppet valve (Fig. 5).
Safety Discs
DHT & DHCR Testers 300 & 400 lpm Models
The loading valve is fitted with two safety discs which are designed to rupture internally at
approximately 7 bar (100psi) over the maximum pressure. When the discs fail, the loading
valve becomes inoperative and the oil flows freely downstream.
To replace the safety discs remove the loading valve assembly from the flow block. Unscrew
the safety disc holder from the valve by carefully gripping the valve on the 30 mm diameter.
Remove the disc spacer and the ruptured discs from the valve and disc holder. Carefully
preform the two discs by pressing them by hand between the disc holder and spacer then place
one new disc inside the valve and replace the spacer.Place a second disc on top of the space
and screw in the disc holder (Fig. 6). Tighten the holder to 40lb. ft. (54 Nm)
15
Fig. 5
Fig 6
Anti-Rotation pin
‘O’ Ring
Spacer
Disc
Disc holder
Grip on this Diameter
Disc

Loading Valve
DHT & DHCR Testers 500 lpm & above
If the loading valve becomes difficult to turn under pressure or will not close, remove the 4 bolts.
Check for worn valve seat, damaged or leaking seals and contamination. Note: If the pressure
does not increase progressively when the loading valve is operated, check if the safety discs
have been ruptured. Assemble the loading valve into the flow block ensuring that the guide pin
is located in the slot on the poppet valve (Fig. 7).
Safety Discs
DHT & DHCR Testers 500 lpm & above
The loading valve is fitted with two safety discs which are designed to rupture internally at
approximately 100psi (7 bar) over the maximum pressure. When the discs fail, the loading
valve becomes inoperative and the oil flows freely downstream.
To replace the safety discs remove the loading valve assembly from the flow block. Unscrew
the safety disc holder from the valve by carefully gripping the valve on the 35 mm diameter.
Remove the disc spacer and the ruptured discs from the valve and disc holder. Carefully
preform the two discs by pressing them by hand between the disc holder and spacer then place
one new disc inside the valve and replace the spacer.Place a second disc on top of the space
and screw in the disc holder (Fig. 8). Tighten the holder to 40lb. ft. (54 Nm)
16
Spacer
Disc
Disc holder
Grip on this Diameter
Disc
Fig 7
Fig 8

17
Remote Flow blocks available for all models:
Consult sales office for details
Temperature 10 - 120 °C (50 - 250 °F)
Internal & External Speed 300 - 6000 rpm
TH3 Photo Tacho.
Gauge 1/4” BSPF (English) 1/4” NPT (American)
Accuracy Flow 1% of indicated flow reading over the top 85%
of the range in the preferred flow direction. Reverse flow testing 1% full scale. Flowmeter
calibrated with mineral oil, viscosity 21 centistokes.
Speed Above minimum speed rating 1% of maximum
speed
Pressure Within 1.6% of full scale
Temperature ±1°C
Battery Tester 9 Volt battery, size 18 x 25 x 43 mm. PP3 (UK),
64F22 (Europe), 6AM6 (Japan) A1604 (USA)
Note: Tester Displays lpm, USgpm and IMPgpm. *Consult sales office for intermittent operation up to 420 bar, 6,000 psi.
Specification
Pressure Gauge, 0 - 420 bar / 0 - 6000 psi
Working Ports
Models Pressure Flow Range
(bar) (lpm) English American
DHCR 60 0 - 420 3 - 60 Tester inlet/outlet 3/4”-14 BSPF Tester inlet/outlet 1” 1/16-12 UNF SAE O-Ring
DHCR 150 0 - 420 5 - 150 Loading valve outlet 1/2”-BSPF Loading valve outlet 3/4”-8 UNF SAE “O”Ring
DHT & DHCR 302 0 - 420 8 - 300 1”-12 BSPF Parallel 1”5/16-12 UNF SAE “O” Ring
DHT & DHCR 402 0 - 420 10 - 400
DHT & DHCR 602-F 0 - 350* 20 - 600 1” 1/2 SAE type four bolt flange
DHT & DHCR 802-F 0 - 350* 20 - 800 Solid 350 bar/5000 psi, Split 200 bar/3000 psi
DHT & DHCR 802-S 0 - 480 20 - 800 1” 7/8 UNF

Designed and produced by the Marketing Dept. Webtec Products Ltd. DH-MA-ENG-1676.pdf 04/06
Webtec Products Limited reserve the right to make improvements and changes to the specification without notice.
Nuffield Road, St. Ives,
Cambridgeshire, PE27 3LZ, UK
Tel: [phone]
Fax: [phone]
e-mail: [email protected]
http//:www.webtec.co.uk
Certificate No.8242
Webtec Products Limited
1290 E Waterford Avenue
Milwaukee, WI 53235, USA.
Tel: [phone]
Fax: [phone]
e-mail: [e-mail]
http//:www.webster-inst.com
Webster Instruments
An der Palmweide 55, 44227
Dortmund, Germany.
Tel: [phone]
Fax: [phone]
e-mail: [email protected]
http//:www.webtec.co.uk
Webster Messtechnik
120 Avenue de Dunkerque
59400 CAMBRAI France
Tel: [phone]
Fax: [phone]
e-mail: [e-mail]
http//:www.webtec.fr
Webtec SARL
For Sales & Service contact: