Hydraulic Power Unit - Multi-circuit Design With Variable Pump Control | Optimized For Efficiency And Synchronization

HYDRAULIC POWER UNIT :

General Information :

A Hydraulic power unit is functioning as a brain of the body
whereas cylinders are muscle power of the system. To design and select the
components solely depends on the application requirement which includes sequence
of operations , time cycles , level of accuracy desired in the final component,
cost factor, and functional requirement.

There are variety of hydraulic circuits standardized keeping
in view the industrial applications. And these can be further modified whenever
needed.

Types of circuits :

1. Basic :
   Single Pump design- Fixed displacement Pump : This is applicable
   when slow speed throughout full stroke of cylinders is a requirement. If
   you desire to have heavy force and high speed with the help of single pump
   fixed displacement pump, you will need to give more power.
2. Double Pump Circuit : During the travel of
   cylinders, cylinder exerts force only when resistance is encountered. In
   first phase till the cylinder touches the job, it will be free movement
   and this we call as approach travel. Similarly during retraction we only
   need little force to carry the weight of platen and or toolings. This type
   of circuit feeds the flow from both the pumps during approach and
   retraction stroke and during pressing operation one pump gets cutoff
   diverting the flow to tank. This cutoff of pump flow can be either
   pressure based or position based. This will help reduce power requirement
   but power-pack capital cost will increase to certain extent.
3. Pre-fill Circuit : This again a concept for
   saving the power requirement. This circuit is normally employed for heavy
   capacity presses. The power saving is achieved with putting extra small
   sized cylinders for movement of platen during approach and retraction
   requiring small capacity of pump flow. During approach, the main cylinder
   is filled through a pre-fill valve plus an overhead oil tank provided on
   the top of cylinder. During Pressing , the main large bore cylinder is
   pressurized with a small amount of oil flow capacity giving a very high
   output force. This will help reduce power requirement but power-pack
   capital cost will increase to certain extent.
4. Variable Pump Circuit : These are the ideal choice for power
   saving because these pumps are giving the flow as per the load requirement
   during operations and hence very efficient as far as energy saving is
   concerned. The flow will automatically get reduced when force is a
   requirement and flow will automatically increase whenever there is a
   little requirement of force ( pressure ). The pumps are costlier in Indian
   market and hence not widely used in all the equipments.
5. Synchronization of cylinders : This is a very
   typical requirement and to have a high level of accuracy we need to
   incorporate electronics with hydraulics. A proportional flow control
   valves, linear scales, PLC unit with comparator circuit and driver card of
   proportional valves are needed. The simplest of all is to couple both
   cylinders mechanically but it is not feasible in all cases. Employing 2:1
   ratio pair of cylinders can also be incorporated in certain applications.
   Moreover we may utilize a pair of double ended cylinders also to achieve
   synchronization.