Nexoil - Dual-Line Valves


Dual-Line Grease Valves

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The system consists of 6 essential components:

  1. Manual or automatic volumetric pump and lubricant reservoir.
  2. Reversing valve, which enables lubricant to be dispensed alternately down each distribution main, allowing the pressure remaining in the unpressurised line to properly decay.
  3. Twin distribution main lines, to convey the lubricant to the feeder blocks.
  4. Feeder blocks which dispense lubricant in precise amounts as the bearings require and
  5. Tail pipes for connecting the feeder blocks to the bearings.
  6. A pressure transducer to indicate to the control panel the end of a completed lubrication cycle.

The feeder blocks should be placed as near to the lubrication points as possible; each feeder block element has 2 pistons, which are hydraulically operated by the pump. One piston acts as a slide valve and directs the flow of lubricant from 1 side of the dosing piston to the other. The stroke of the dosing piston is fully adjustable from zero to the maximum the feeder block is designed to dispense.

The main line, which connects the pump to the feeder blocks, should be sized to accommodate an NLGI 2 grease flow of 70 kg per hour and an operating pressure of 160 bar. However, in certain conditions and with high-pressure equipment these recommendations can be exceeded. Most important is the positioning of the main lines which should take into account the need to protect the mains from damage and, furthermore, the need to remove equipment to which the mains may be secured for repair.

A further element to be considered, in the event of an automatic pumped system, is the need to program the operation of that system. This can be achieved with extremely basic equipment, which will merely switch on the pump at the appointed time and switch the pump off on completion of a cycle; alternatively, a sophisticated method of programming and recording the successful operation which also indicates visually and audibly any major malfunction can be selected.



The operation of the distribution valve and pipe-work layout is clearly illustrated above.

Both upper and lower main lines are connected to a pump and feeder blocks. The position of the reversing valve ensures the upper main line is under pressure when the lower main line pressure is in decay, and thus the lubricant in this line returns to the reservoir.

When the distributor pistons of all the feeders in the system have operated, the pressure continues to rise until the system pressure is reached. The system pressure is that which is required to operate the feeder block that is either furthest from the pump, or with greater restriction through the pipe-work, plus 25% increase on the pressure reached. This allows for any changes in the viscosity of the oil or the apparent viscosity of the grease due principally to temperature changes. At this point, the reversing valve changes the direction of the pump flow; the upper main line, which was under pressure, is now in decay, the lower main line that was in decay is now the pressure line. The increase in pressure causes the slide valve to be displaced in the opposite direction, opening the port to the feed distributor piston. As the pressure continues to rise, the feed distributor piston displaces the lubricant that created the previous displacement out through the outlet to the bearing, thus returning the feed block to the position at the commencement of the cycle. A full lubrication cycle is now complete.

The flow of lubricant to the bearing from the dispensing valves is dependent on the stroke of the dispensing piston, which can be adjusted in accordance with the bearing requirements. The adjustment is carried out by reducing the stroke of the dispensing piston with the metering screw situated in the turret of the metering chamber. The regulated amount will be dispensed equally to each of the outlets from that element of the dispensing valve.

An indicator rod secured to the dispensing piston gives a visual indication of the dispensing valve's operation. However, where there is an extremely hostile environment, ie sinter plants, underwater, fertiliser plants, etc, the indicator rod can be dispensed with to ensure a totally enclosed contamination-free system. Under these circumstances, regulating the outflow of lubricant is not possible.

As previously stated, each element is capable of supplying to individual application points. Although the amount of lubricant dispensed is common to both ports, the feeds are totally independent and do not rely on the successful operation of one to ensure the successful operation of the other and this is true of the whole system. Each application point is totally independent of the rest of the system.

If required, the 2 outlets from a single element can be joined internally or externally for the feeding of one point only. This arrangement is used to feed bearings larger than the output of a single element and prevents the mixing of 2 ranges of different output feeder blocks.

The frequency of operation is dependent on a number of factors, all of which are applicable to both hand operated and automatic systems, namely speed and type of bearings, temperatures they operate at, load they are supporting and quality of the lubricant. These are the predominant factors and should be discussed in depth prior to selecting the system and its operating criteria.

Grease Mains Pipework to BS1387 Heavy Grade

It is essential that the bore of the pipework is perfectly clean and free from scale and any contamination. Any pipework to be stored should have the bores internally oiled and ends capped. All bends and offsets must be cold formed to prevent the development of scale.

If heat is used to either bend the pipe or backweld the fittings, the pipework should be pickled in acid to remove the resultant scale and neutralised, prior to the introduction of lubricant. If the pipe is being stored, it should also be oiled internally and ends capped.

Ensure brackets are secured to the pipework prior to and after every bend and offset. Straight lengths should be secured in accordance with BS4807

An alterative to BS 1387 steel pipe and wrought iron screwed fittings could be, seamless hydraulic pipe and compression fitting

Wrought Iron Screwed Fittings to BS1740 Part1

Wrought Iron Screwed Fittings to

Copper Intermediate Mains and Feed Pipes to BS287 C106

These will be supplied in nominal 3 metre lengths and will be half hard. They should be secured In accordance with BS4807.

Copper Intermediate Mains and

Brass Compression Fittings to BS 2051 Part 1

These should be the cap nut bonnet type fittings with BSP internal and external threaded connections.

Brass Compression Fittings to

CLASSIFICATION OF GREASES (National Lubrication Grease Institute)

CLASSIFICATION OF GREASES (National Lubrication Grease Institute)

The penetration index expresses the depth of penetration, in tenths of millimetres, of the mass of grease being measured in a penetrometer.

Use the softest grease with good flow characteristics and temperature stability that the application will allow.

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