How to select the right Hydraulic Flow Divider

Despite being constructed from the same standard components, Slack & Parr flow dividers can be used as an:

• Equal flow divider: to divide a supply flow into a number of equal separate streams (2 to 6 divisions is usual, but more can be achieved for special applications)
• Unequal flow divider to divide a supply flow into a number of unequal streams
• A pressure intensifier can provide a higher pressure for part of a supply flow.

Each application needs a slightly different approach to be taken when calculating the sizing selection. For new systems design, the supply can also be defined after the flow divider. However, if a flow divider is to be retro-fitted into a system the existing supply must be taken into account.

In cases where the supply flow rate is known, the steps to be followed are:

1. Divide the supply flow by the number of divisions required;
2. Convert the flow units to cc/minute;
3. Divide this cc/minute by the optimum speed of 1500 rpm;
4. Select the nearest element size available;
5. Check exact operating speed for this size.

As an example, using a 2-way flow divider, to split the oil supply 50:50:

• For a supply flow of 1000 litres/hour, each half will be 500 litres/hour;
• 500 litres/hr (divide by 60 and multiply by 1000) is 8333 cc/minute;
• Dividing this 8333 cc/minute by the optimum mid-range speed of 1500 rpm (8333 / 1500) translates to 5.55 cc/rev;
• The nearest element size available in this case is 6 cc/rev;
• We can check the exact operating speed by dividing the split oil flow (here, 8333 cc/min) by 6 cc/rev: 8333 / 6 = 1388 rpm which is within the optimum speed range.

In cases where the individual delivery flow rate is known:

1. Convert the flow units to cc/minute;
2. Divide this cc/minute by the optimum speed of 1500 rpm;
3. Select the nearest element size available;
4. Check the exact operating speed for this size.

The principle of selection is similar to that for equal flow dividers:

• For each unequal flow rate pick an element size that gives the nearest to 1500 rpm;
• Bear in mind that each element will rotate at the same speed as the others, and also that FDR flow divider elements cannot be mixed with FDL elements;
• Consider what combinations of element sizes will give the ratios of flow needed – three equal elements can give a 2 to 1 ratio for instance;
• After selecting the element numbers and sizes, re-check the speed is within the optimum (or if necessary, the working) speed range.

Alternatively, contact our technical team; they will be able to help you select the right configuration for your required flow ratio.

Let’s work through an example, using a 2-way flow divider to split the oil supply 60:40:

• For a supply flow of 1000 litres/hour, one side will be 600 litres/hour and one side will be 400 litres/hour
• Firstly, 600 litres/hour (divide by 60 and multiply by 1000) equates to 10000 cc/minute
• Divide this cc/min (10,000) by the mid-range (optimum) speed of 1500 rpm (10000 / 1500) = 6.66 cc/rev.
• Then 400 litres/hour (divide by 60 and multiply by 1000) equates to 6666 cc/minute
• Divide this cc/min (6666) by the mid-range (optimum) speed of 1500 rpm (6666 / 1500) = 4.44 cc/rev.

In this case, the nearest available element sizes are 6 cc/rev and 4cc/rev.

• Bearing in mind that each element will rotate at the same speed as the others, check the exact operating speed: divide the split oil flow (10000 cc/min) by 6 cc/rev: 10000 / 6 = 1666 rpm.
• The 4cc will automatically be rotating at the same speed.
• This is within the optimum speed range.