How is your hydraulic heat exchanger connected?

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Heat, or more precisely overheating, is public enemy #1 of hydraulic equipment. The component we most depend on to maintain acceptable and stable operating temperatures in a hydraulic system is the heat exchanger. Unfortunately, it's often considered an 'accessory' - indeed most major manufacturers even catalogue them this way. As a result, the heat exchanger is often installed in a hydraulic system as an afterthought - wherever it will fit, and plumbed up in the most convenient, rather than the most efficient way.

For example, air blast heat exchangers should be situated so that they are at least half the fan diameter clear of any obstructions on both sides of the core. I recommend connecting the exchanger so that hydraulic oil flows from bottom to top, or if the tanks are on the sides, from lower connection (inlet) to upper connection (outlet). The reason for this is to purge all air from the unit quickly and fill it completely for maximum efficiency.

The other connection issue for air-blast heat exchangers, which requires attention during initial installation, relates to whether it is single or double pass. These days, many exchanger cores are designed so that they can be configured as either single or double pass. This means they have at least 3 ports - two ports in one tank and one port in the other (see diagram below). A single pass exchanger is converted to double pass by the insertion of a fully welded baffle in the middle of one of the tanks at the factory. This makes the oil flow down one half of the exchanger core, and then back up the other half.

Hydraulic heat exchanger with 3 port connections

Considering the above diagram, if the exchanger is single pass (no baffle in the top tank as shown), I would connect the exchanger so that port 1 is the inlet and either port 2 or port 3 (but preferably port 3) is the outlet. HOWEVER, if the exchanger is double pass (as shown above), the correct connection is port 2 inlet; port 3 outlet (or vice versa).

Note that if the unit is double pass and the hydraulics technician doing the initial installation is not on the ball, he'll likely connect the unit in such a way that port 1 is used. Doing so means that only half the exchanger is effective. That is, if connection is made using ports 1 and 2, only the left-hand side of the cooler is effective. If connection is made using ports 1 and 3, only the right-hand half of the cooler is effective. And believe it or not, I've seen this happen more than once. But it's not hard to detect this mistake - due to the large temperature variation between the two sides of the exchanger.

So the next time you're working on a hydraulic machine, take note how the cooler is installed and connected. Could the installation have been improved? And even though the probability is low that the machine has a double pass exchanger which has been connected incorrectly, use your heat gun to confirm that the temperature drop across the cooler is even across its core.

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