4 min read

Is Choosing a Sample Port Location Driving You Mad?

Mon, Jul. 07, 2014

Mad ScientistThe ideal sample port location depends on the purpose for drawing the sample. There are several reasons to draw samples from your hydraulic or lube systems. The main reason is to ensure that the fluid traveling through your system is not loaded with contamination that will damage your pumps, valves and other components.

Secondary reasons include identifying components that are beginning to wear before they fail (this allows you to be proactive about the component replacement or repair) and verifying filter element performance. Continue reading to learn where to take a sample from for each of these reasons. We’ve also included some general fluid sampling tips at the end of this blog.

Identifying Fluid Cleanliness


Your main sample port should be drawing directly from the reservoir to provide the most representative sample of the fluid traveling through your system. When your ISO codes rise, draw samples from the secondary locations to identify where the contamination is originating.

Kidney Loop

A sample port before the filter on a kidney loop enables you to verify the condition of the oil that is traveling from the reservoir to the pump. If the fluid coming from the reservoir is not meeting your target ISO code you should change filter media to capture more of the contamination.

Return Line

A sample port on your return line will tell you the condition of fluid returning to your reservoir. Some technicians use this as their main sample port. We would not recommend this, as the slow flow rate can necessitate the use of a vacuum (vampire) pump to pull the sample. We’ll explain why we prefer not to use vacuum pumps when sampling in the General Sampling Guidelines section later.

Verifying Filter Performance

Filter Assembly

Install a sample port after a filter assembly to ensure the element within is living up to your expectations. If you find that it is not, check for leakage in the bypass valve and the other valves in the assembly. If the valves are not leaking and your fluid is not as clean as you would like, it’s time to change filter media.

Identifying Failing Components

Placing a sample port after each valve, bearing and pump will allow you to identify when a component is wearing so that you can schedule a repair instead of performing a corrective action and replacement after it fails. The return on the initial investment will be quick as you can now avoid corrective maintenance and allow yourself to perform mostly scheduled maintenance. Now you’re responding instead of reacting, avoiding unscheduled downtime and increasing productivity and efficiency.

General Sampling Guidelines

Preparing a Sample

Follow the steps below to draw accurate and consistent samples:

1. Attach a hose to the sample valve. 
Position the open end of the hose over a bucket to catch the fluid. 

2. Quickly open and close the sample port three times to flush the valve out.
On the fourth time, leave the valve open. 

3. Remove the cap from your sample bottle. 
Keep the surface of the lid that will come in contact with your fluid pointed down to avoid it becoming contaminated with airborne fallout.

4. Flush out contamination from your sample bottle. 
Fill the bottle halfway with the fluid you are sampling. Secure the lid and agitate. Empty bottle into bucket. Repeat 3x in total. 

5. Draw your sample and secure the lid. 
Fill the bottle to the bottom of the throat (85%).  


If you are placing your sample port on an elbow, the sample port should be in-line with the direction the fluid is coming from. If the fluid makes a turn before entering the port, you will miss the large particles as they are shifted to the outside of the elbow as they travel through it.


There’s no filtration on a gearbox so how do you pull a sample? A kidney loop should be installed on every gearbox to maximize the life of the unit. The sample port should be between the gearbox and the kidney loop so that you know the condition of the fluid before the contamination is removed from it. If you cannot install a kidney loop, use a filter cart to pull your sample. Pull the sample before the filter as soon as you turn on the cart.

Vacuum (Vampire) Pump

We prefer not to use a vacuum pump because fluid picks up contamination from everything it comes in contact with that is not actively cleaning it. A vacuum pump is another opportunity for your sample to become artificially contaminated causing you to believe that the fluid in your system is not as clean as it actually is.


Need help selecting your target ISO code? Download our free ISO Code Target Selection Chart.


Written by Jim Harlan


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