"B" "LR" "S" & "POWER PLUS" SERIES HYDRAULIC TESTING

"A WORD OF CAUTION"

It is expected that the following information is used for the purpose it was intended. The information is intended to be used by qualified Technicians who will not only be able to interpret the recorded data but who will conduct the tests in a safe and workman like manor. We cannot emphasise enough the use of sound safety practices.

Generally the testing can be carried out on Bomford Turner hydraulic flail mowers and hedgecutters with the following equipment

1/ HYDRAULIC FLOW METER/PRESSURE GAUGE

The flow meter should have the ability of measuring flows of up to 180l/m, pressures of up to 400 bar ( 5800psi ) and ideally have a temperature gauge incorporated within the system. A loading valve must also be available within the unit.

The feed and return ports should be in the order of 1" BSP.

2/ TACHOMETER

This may be of either a strobe type or a mechanical direct reading type. It should be capable of measuring 4000 rpm.

MACHINE MODEL

The machine base designation will help you a great deal in understanding not only the reach of the machine but also the hydraulic capacity of the motor drive system.

EXAMPLE 1:   B54MPS Power Plus

B    "B" SERIES MACHINE

54    5.4 METRES OF REACH TO THE END CUTTER

MP    MECHANICAL PARALLEL

S    SLEW

POWER PLUS    125 LITRE SYSTEM

EXAMPLE 2:   B608

B    "B" SERIES MACHINE

60   6.0 METER REACH

8     84 LITRE HYDRAULIC SYSTEM

EXAMPLE 3:   B80M POWER PLUS

B    "B" SERIES MACHINE 

80    8.0 METRES REACH 

M    MID POSITION CUTTING HEAD 

POWER PLUS    125 LITRE SYSTEM

"B" designated machines indicate the reach mostly in metres. Where the reach number is repeated the machine is able to cut on both sides of the tractor e.g. B45-45 or B81-81. These machines will cut this distance on each side of the tractor from it's centre line to the extreme flail.

"LR" designated machines show the reach directly in feet.

"S" designated machines again indicate the reach in feet.

Where "T" is used as a suffix it may denote that the machine is a twin pump unit. However in latter years most machines are twin pumped and the "T" will probably denote that the second arm is a telescopic arm. The letters EPP (Electronic Parallel Proportional) are used to indicate the electronic proportions controls on the machine.

We therefore have the following hydraulic systems.

Rotor feed and return pipe are either 1"BSP or ¾" BSP. All 207 bar machines have as a minimum double wire pressure hose. The piston machines with a relief valve setting of 275 and 350 bar having a minimum of triple wire pressure hoses. All unions are swivel nuts with male soft seal cones. This relates to an "O" ring sunk into the male cone. All machines with the exception of some B577, B73-73 and B83-83 are to the BSP standard, these exceptions are built to the JIC standard.

TEST PROCEDURE

This information is essential if any of the machines are to be evaluated hydraulically. All tests should be conducted at a temperature as close to 40 degrees centigrade as possible.

The flow meter should be inserted in place of the motor. This diagramatically looks like the sketch below.

PUMP TEST LAYOUT

All Bomford Turner pump specifications are rated at a PTO shaft speed of 540 rpm except for the Eaton piston systems, these are rated at 1000 rpm. This speed, in most cases, is increased 3 or 4 fold to achieve the desired pump speed. It is therefore very important to ensure that the tractor PTO shaft is in good working order and that the tractor engine has enough power to maintain the 540/1000 rpm at full power. Errors through the transmission are multiplied by this same ratio. Running the test in the 1000 rpm ratio at the 540 speed can and does reduce the power available from the tractor. It is therefore possible that the tractor will stall when using this arrangement.

With the flow meter in the circuit, the PTO shaft at the correct speed, we can now take the no load reading of the pump from the flow metre. That is zero pressure but maximum flow. This nominally will be at any of the system flows i.e. 70, 84, 100 litres etc.

For the next step you may find the graph on page 6 useful. We have now to establish the efficiency of the unit. By plotting pressure against flow we can accurately do this. Fig.I shows the plot of two hydraulic pump outputs. Naturally if we only had the one set of figures then a bad pump would not be quite so obvious. The simple calculation in Fig.II can then be used to highlight the deficiency of the unit. We can therefore calculate this efficiency or by experience, look at the shape of the graph to illustrate the pumps condition, i.e. the flatter the curve the better the pump. Conversely the steeper the gradient of the graph the lower the efficiency. The graph shows a typical output for a gear pump, a piston pump will be flatter with little fall off in the early stages of testing.

To achieve the figures for this graph the loading valve is wound in to increase the load on the pump. At say 25 bar increments note the flow output of the pump in litres. These figures are then transposed into the graph form.

Pressure is only achieved by the action of work done. A pumps output is not measured in pressure but capacity. The power equation is a product of the flow and the maximum operating pressure multiplied by the efficiency figure. This will help in the identification of a poor hydraulic unit. The level of acceptability in some way will depend very much on just what the machine is being used for, e.g. the lower pump as on the graph below is absolutely worn out and not much use to anyone. However if a pump is giving a little lower than expected output then it may well be satisfactory for the lighter duties but it should be remembered that once the output falls it is only a question of time before we have a total failure. We would consider that any deficiency figure over 15-16% is too low for general operations. Progressive overheating will occur, the severity of which will depend on the deficiency figure.

Generally, even a bad pump may achieve the maximum pressure rating. However this is no good without a good flow output. The maximum pressure setting being reached will only indicate that the pressure relief valve is set correctly and in working order. The relief valve should hold pressure to just under it's full flow setting. The relief valve will then "crack" at this lower setting- something like 10 bar below the maximum. This is designed in to prevent high pressure peaks or over shoots when the valve opens. The relief valve will close once the pressure has fallen to below 90% of it's maximum setting. Failure to allow the relief valve to close will result in excessive overheating of the system. This often comes about where the operator is using one of the smaller powered machines in grass at higher speeds than should be used. In most cases this will conclude the test for the pump, however if the relief valve is under suspicion then the same test should be conducted without the relief valve in the circuit and the results compared. Care should be taken not to over pressurise the pump as damage will result.

The motor is now the next major component to consider. It should be noted that the other components should be tested out before moving on to the motor. The motors fitted to Bomford Turner products fall into four categories.

There are various methods of testing the motors efficiency but as we have varying standards of motors we will adopt the safest method that can be used on all types of motors. It should be noted that in instances were no drain line is fitted any pressurisation to the return line will blow motor shaft seals.

The hydraulic test unit should now be placed into the return line of the circuit as below. 
Ensure that the test unit loading valve is wide open,

With the tractor engine stopped, stall the rotor drive. This can be achieved by using a large timber post securely held between the rotor, cowl and the ground. It is important to secure the rotor firmly and safely before progressing further. It should be noted that wedging the rotor with the direction of rotation will draw the post into the cutting head locking the rotor. This is the correct way of stalling the rotor. Under no circumstances wedge the rotor against the rotation of the rotor.

The tractor engine and PTO should now be engaged and increased to the rated speed. Gradually engage the motor drive circuit. Naturally the relief valve will blow at it's pre-set setting. The oil flow through the stalled motor is the motors "slippage" and hence it's inefficiency.

however

Again, as with the pumps acceptable efficiency much will depend on the work the machine is doing. However, anything above 15-16% should be considered a poor reading and a motor change should be considered. Overheating will result with an inefficient motor just as with a worn pump. It is possible to gain some idea of a motors performance by using a tachometer direct onto the rotor shaft. This is known as the free air turning speed. Again the PTO shaft must be set to the correct speed and with the pulley guard removed, place the tachometer direct onto the rotating rotor shaft. Readings should be taken with the pulleys set in their fastest condition i.e. large pulley driving small.

The nominal rotor shaft speeds are listed below.

A poor motor will show a reduced rotor speed, unfortunately this method is not reliable and does not relate to any efficiency figures.

Fig. I

Fig.II

In the lower graph we can conclude the following:-

By all accounts a very poor pump output at 78% deficient. The upper line is the result of a test conducted on a good pump. It is therefore apparent that the area contained between the two graphs is the area representing the pumps deficiency.

In the upper graph we can conclude the following:

SUMMARY

These tests are the very basic tests that any technician should know in order to asses the condition of one of our hydraulic flail units. There can be other influencing factors which may lead the technician onto the wrong track. For example; a slipping tractor PTO clutch, poorly sealing suction hose allowing air to be drawn into the circuit, a crushed suction hose and water in the oil, probably as a result of condensation or reckless pressure washing the tank top, or any other contaminant. Return line filters on their own are seldom a reason for poor performance. However long term neglect of filters will cause expensive premature wear of major components. When filter elements become blocked they by-pass un-filtered oil. This by-pass valve is set at a low pressure (1 to 2 bar ) so cannot contribute to any power losses. It should be noted that these systems are seldom totally sealed. Those systems with twin pumps, the second pump being used to power the rams, can by the very nature of the working ram draw small fragments of contamination into the system. Our filters are designed with enough capacity if regularly changed to accommodate this. However a blocked filter does not filter at all. Filter change intervals should be implemented at the following intervals:

It should be noted that neglected filter changes contributes to something like 80% of all the hydraulic problems encountered. A fact that should not be ignored.

"A WORD OF CAUTION"

It is expected that the following information is used for the purpose it was intended. The information is intended to be used by qualified Technicians who will not only be able to interpret the recorded data but who will conduct the tests in a safe and workman like manor. We cannot emphasise enough the use of sound safety practices.