Tramp Oil Skimming and Metal Working Fluid Management FAQs

This section of the site is designed to help you understand metalworking fluids and how our coolant maintenance products will serve your objectives. Please let us know if we may be of any further assistance by calling 888-249-4855

Mixers

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Why can’t a venturi mixer, such as the Zebra Economy Mixer or Machinist Mixer, deliver the coolant mix through a garden hose to all the machine sumps?

A venturi mixer pulls the coolant concentrate via pressure created by the water source, then mixes it with the water in the inner chamber. When attaching a garden hose to the outlet of a venturi mixer, the water pressure is instead used to push the column of fluid through the hose, resulting in a loss of coolant concentration, or none at all.

The Zebra Proportioning Pump is required for long distance coolant mix delivery such as through a garden hose or even through hard conduit. It works by a process called positive displacement whereby a piston is moved by the water pressure. Each time the piston moves, it draws a given amount of coolant concentrate which is then mixed with the water through the hose or conduit. Therefore, it does not lose its ability to pull concentrate even though it is also pushing the column of fluid. The Zebra Proportioning Pump will be able to mix and deliver the coolant mix up to 800 feet laterally, and up to 20 feet vertically! We recommend utilizing a check valve on the outlet side for any vertical installation so the column of fluid does not create back pressure to the pump.

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I have the Zebra Machinist Mixer (P/N MIX03725) and I have the dial set at 7 but I am getting a 15% concentration. Is the mixer defective?

No, the mixer is not defective. The numbers on the dial are for reference only, and not an actual calibrated scale. The Machinist Mixer uses a venturi to create a vacuum which draws the concentrate through the standpipe to then mix with the water. It does this using the water pressure on the incoming side. The concentration on the output side will depend upon your concentrate’s viscosity as well as your incoming water pressure.

You will need to verify the outcoming mixture with a refractometer, then make any necessary dial adjustments. To note, we recommend installing a pressure regulator on your water inlet if you have changing water pressures. This will ensure the correct output concentration, once set by the dial. It is also recommended to use the Mixer Lockout if operators are unaware of this, or if outright tampering is an issue.

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Why is it recommended to install a water filter for the Zebra Proportioning Pump?

The proportioning pump has many small parts which can wear if given the opportunity. Using a pre pump water filter will decrease the likelihood of wear since it will capture any tiny particles that may flow through your water line.

Refractometers

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I am trying to determine the best refractometer for my application. There are various scales to choose from. How do I know which one is suitable?

Refractometers use a scale called the Brix Scale. This scale was initially designed for measurement of sugar content in a water solution, but it is still used for metalworking fluids. Some coolant manufacturers make their blend so it measures 1:1 with the Brix Scale. Some do not. Check the product data sheet for your coolant’s “refractometer factor”. You will need to multiply this factor by the reading you see on the scale to determine the actual percent concentration of the solution. But, to determine which scale is the best, you will need to divide the required concentration(s) by the refractometer factor.

So, say your refractometer factor is 1 and you need a 10% concentration. You will only need a scale that goes up to 10 (10 / 1 = 10).

But, say your refractometer factor is 2 and you need a 8% concentration. You will only need a scale that goes up to 4 (8 / 2 = 4).

Yikes...you need a 20% concentration and your refractometer factor is 3.7! You will need a scale that goes up to 5.4 (20 / 3.7 = 5.4).

It is recommended, however, to use a scale that has a higher range than what you are trying to achieve, since evaporation at the sump level will increase the concentration. You will then be able to read whatever concentration the sump is at.

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I have a refractometer with a scale of 0-10. My coolant is supposed to run at 8%, but when I check it with the refractometer, I see nothing registering on the scale. What’s the deal?

Your concentration is way too high and off the chart!

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One of the refractometers I have reads 1% lower than all the other ones in my shop, even though the concentrations are all the same. Why is this?

This refractometer probably needs to be recalibrated. Use water (tap water is okay, but distilled is best) to zero the scale (in accordance with the instructions for your unit), then try it again.

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When I put a drop of coolant on my refractometer, it is so blurry I can barely make out a reading. Does this mean that I need to replace it?

It means you need to replace the coolant in the sump, and not the refractometer. When a definitive reading is not possible, the sampled coolant has deeply emulsified tramp oils in it. It is still usable for the lubrication process, but may promote excessive coolant mist, feed bacteria which degrade coolant, and contribute to health and safety issues. Not to mention you'll never be certain of its concentration. Your call.

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Why does the concentration of a sump increase even though the same concentration is used for each refill?

At the end of the shift, the missing volume of a sump is not only due to carry-off. It is also due to the evaporation of the water within the mixture during the machining process. Since water composes up to 95% of the volume, even a slight evaporation rate can change the overall concentration significantly. You will need to do a calculation by volume to determine the appropriate concentration for the refill.
Please refer to the example below. To note, evaporation rates may be different between machines and/or processes. It is best to calculate this rate per machine sump and per process to ensure consistent concentrations.

Example
Known Factors:	Desired Sump Concentration: 5% Total Sump Capacity: 50 gallons Volume of Make-up Solution Needed: 25 gallons Current Sump Concentration: 8%
Unknown Factors:	Required Make-up Concentration
Calculation:	Determine the volume of concentrate needed for the entire sump (volume of 50 gallons at the desired concentration of 5%): (.05 x 50 = 2.5 gallons of concentrate) Determine the volume of concentrate needed for a make-up solution if only 25 gallons are remaining in sump at 8% concentration: (25 x .08 = 2.0 gallons of concentrate) Then (2.5 gallons of concentrate originally in entire sump) -2.0 gallons in remaining sump .5 gallons of concentrate needed for make-up Determine concentration for make-up solution: (.5 gal of conc. ÷ 25 gal fluid required = .02, or 2% conc.)
Answer:	The sump now needs to be filled with a 25 gallon make-up batch at a concentration of 2%.

Hardness Testing Sticks

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My coolant separates out of the water after mixing it. Why is this happening?

This is due to an excessive amount of minerals in your water supply (also known as hard water). The abundance of these minerals (mainly calcium and magnesium) prevent, on a chemical level, the concentrate from remaining in the mixture. It is possible, even with softer water, for there to be an abundance of these minerals over time, due to the effects of evaporation at the sump level.

If this is a consistent issue, use the Zebra Hardness Testing Sticks to check the level of your water hardness and compare it to the product data sheet for your coolant. Most coolant manufacturers will specify what hardness range their blend can withstand. If your coolant is outside the range, you can use an additive to decrease the hardness, or even consider RO (reverse osmosis) water.

Hard water can also contribute to surface grease formation, which is not readily removed via mechanical skimmers since its surface tension is different than that of straight oil. Coalescers would work better for their removal. Grease formations also contribute to premature filter blockage.

Other negative factors due to hard water are rust and gummy residues, either on parts or machine interiors.

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Why does coolant foam?

The most common reason for foaming coolants is a lack of minerals in the water supply (also known as soft water). We suggest checking the hardness of your water using our Hardness Testing Sticks. This quick and easy monitoring step will prevent overflowing sumps and help to ensure that, without foam, any tramp oils will separate more quickly on the surface for removal.

The second reason for foaming coolant is over-aeration. This can be caused by high pressure delivery systems and/or piping routes (never use a 90° angle) as well as aerating devices, such as our Oxygenator™ (whenever your machine pump is running, you can unplug it without negative sump effects).

Mechanical Skimmers

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My mechanical skimmer no longer picks up oil, why not?

Mechanical skimmers (disk, belt, or tube type) are designed to pick up oil, and will continue to do so as long as the oil layer IS just oil. Once the pickup mechanism no longer attracts and picks up the surface layer, the layer has become something other than just oil (referred to as biofilm) or it is coated with a rejection chemical.

Biofilms are formed when an abundance of bacteria have colonized. They combine with their food source- the oil layer. Until the bacteria are under control, this mucous layer will grow larger, clog lines and filters, give off foul odors, and eat away at the good stuff in your coolant. Nothing will pick it up except for a coalescer or shop vacuum. It is recommended that the machine be fully cleaned and decontaminated, then recharged with fresh coolant. You will know the machine is decontaminated
when its rinse bath is a pH of 7 (that of water).

A rejection chemical is a chemical that is in your coolant blend or from another source (such as rust preventative or anything else that may end up in the coolant soup). The most common chemical that can cause this rejection is silicone. Once it is wiped off the pick up mechanism, the skimmer will work-but only until it is recoated! We recommend the use of the Muscle Coalescer instead of the mechanical skimmer for this situation.

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What are the benefits of using the Diverter™?

If your mechanical skimmer is not on a timer, it will lift off your coolant too.

Most coolants have some type of oil to their base (ie. mineral oil, vegetable oil, etc.) for lubrication purposes. A mechanical skimmer loves oil, and does not know the difference between the bad tramp oils you need to remove from your sump and the good oils that may be within your coolant base. It will pick up anything it knows as oil...period.

The Diverter does know the difference, and uses gravity separation to separate out the tramp oils form the coolant, and will revert the coolant back to the tank. All you will have in your waste container is tramp oils, saving hundreds of dollars a year in wasted coolant.

However, the Diverter does know the difference, and uses gravity separation to separate out the tramp oils from the coolant, and will revert the coolant back to the tank. All you will have in your waste container is tramp oil, saving hundreds of dollars a year in otherwise wasted coolant.

The other option is to put the skimmer on a timed cycle, so it runs only as long as the oil layer is present. Once the tramp oils are picked up, the skimmer is turned off by the timer. Most often, getting this timed cycle just right is the challenge, and can take several days and a lot of hassle!

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I have only 3 CNC machines in my small shop and money is tight. I need a mechanical skimmer to remove tramp oil from the sumps, but I also would like to skim off a holding barrel. What is the best product for this application?

Either a Zebra Belt Skimmer or Sidewinder™ Tube Skimmer, depending upon the access to your sumps. We recommend also mounting the Diverter and the Lockjaw™ Mounting Clamp. With the Lockjaw, you can then easily move the skimmer set up between each sump as well as to your barrel.

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I have a belt skimmer, but it’s not a Zebra. I think the company went out of business, and I need a replacement belt. Do you have them?

We supply replacement belts for other brand skimmers, but have only the 3/8” cogged, flat poly, or flat steel variety. All we need from you is the width and OAL (over all length or end-to-end) measurement. If you do not have the original belt to measure from, then we have a specifications worksheet which you will need to provide a few measurements of your brand skimmer. We can calculate the OAL from there and get you a replacement to get you back up and running.

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Why can I not buy just a tube for replacement for the Zebra Sidewinder™?

We supply the entire tube cartridge, which also contains the gear set which drives the tube. We have found, in most cases, that the gears also wear and need replacement along with the tube. If your unit had a tube that did not move, for instance, it may not only be a problem associated with wear of the tube, but also of the gear set. The cost of the entire cartridge assembly is still economical and you will not spend valuable time trying to troubleshoot the unit.

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I have an Simple DIsk Skimmer and the motor keeps burning out. Help!

The Simple Disk Skimmer comes equipped, standard, with an intermittent duty motor. That means that it needs time to cool down since it does not have a fan. Run time is 40 minutes maximum with a 20 minute cool down period. If this is a problem for your application, then you can upgrade the motor to a fan cooled type. Give us or your distributor a call for details.

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How do I know if I should get mechanical skimmers or coalescers to remove tramp oils?

It is a matter of what best “fits” your application as well as your equipment preference.

A mechanical skimmer will remove the tramp oil layer via a pickup mechanism, such as a disk, belt, or tube. The tramp oil is then discharged automatically to a waste container, which will need to be manually emptied as needed. Since tramp oils are best removed daily, as they are a food source for bacteria, it is recommended to have one on each machine sump to run as needed.

A coalescer draws in the entire surface layer of your sump, then gravity separates the oil within its holding tank for manual discharge to a waste container. Again, oil removal should be done daily, so dedicate a coalescer (such as a Muscle™) on each sump to run continuously, or daily utilize a portable unit (such as the Snapdragon™) on each sump.

More information on each product selection can be found in their product sections.

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What factors should I address when choosing the appropriate mechanical skimmer?

Selection of a mechanical skimmer is based upon sump or tank factors such as:

Access to the area where oils naturally collect (mount location of the skimmer)
Reach needed to the lowest fluid level (distance from mounting point)
Required rate of oil pickup (quarts or gallons per hour)
Temperature of the solution (as in wash water)

If using a mechanical skimmer, we recommend the use of the Diverter accessory, which mounts below the skimmer to redirect any removed coolant back to the sump or tank. See the Diverter section for details.

If the sump runs only one or two shifts, then we also recommend the use of an Oxygenator™ during the time the pump is down. It will help to prevent bacterial rancidity by keeping oxygen in the fluid. See the Oxygenator section for details.

Coalescers

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What is the benefit of using a coalescer to remove the tramp oil over that of a mechanical skimmer?

A mechanical skimmer only removes the tramp oil and needs regular maintenance to keep the chips and other debris that are collected off of the pickup mechanism and the oil scrapers.

The Muscle™ Coalescer will remove the oil layer AND keep the coolant sump in constant circulation, helping to prevent bacterial contamination which degrades coolant. If the machine tool runs less than 2 full shifts per day, a Muscle Coalescer will help to keep that sump in its best overall condition, preventing bacterial problems and coolant degradation. Little to no maintenance is required, as cleaning of the coalescer only needs to be done if their is a buildup of chips and debris within it, or if it is biologically contaminated. Zebra manufactures models which have chip collection capabilities to remove chips which also help to degrade coolant.

If using a coalescer is impractical or impossible near that machine, use a mechanical skimmer to remove the tramp oil and run an aeration device, such as the Zebra Oxygenator™, whenever the pump does not run to help keep bacteria at bay.

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How do I know that the Muscle Coalescer will effectively separate tramp oil from my coolant?

The Muscle has a hold time of 15 minutes, and with its coalescing media, will be able to separate tramp oil which naturally gravity separates in 20 minutes or less. To determine the amount of tramp oil that will naturally gravity separate in 20 minutes, you will need to take a miniature separation test for each sump.

Using a clean, clear plastic pop bottle, for instance, dunk it in from the top of the sump to the bottom, for a cross section of the solution. Cap the bottle off and shake it vigorously for 10-15 seconds. Then let it stand to naturally reject the tramp oil while timing the process. Whatever tramp oil separated in 20 minutes will be the amount that the Muscle will be able to remove from that sump.

To note, as coolant ages, and the more base oil there is in your coolant, tramp oils will take a longer time to gravity separate. You may find that older sumps take longer for the oils to separate. However, if you were to use the coalescer from the first day of a recharge, it will remove the tramp oil effectively.

Also, add on high-pressure coolant delivery systems cause tramp oils to deeply emulsify into the base coolant because of the pressurization of the solution. During the separation test, you may see mostly a separated inverse layer, somewhat like a milkshake. This may be the only separation, yet this layer is still best removed. If using a coalescer, it is recommended to run the coalescer only when the machine pumps are not operating, whenever possible, for the best effectiveness.

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Are there limitations to using the Muscle Coalescer on multiple machine sumps?

We supply the Muscle with a small submersible, centrifugal pump so it can fit into most machine sumps. It is pretty rugged for most applications, however, it is not designed to handle a lot of air intake. If reintroducing this pump to every machine every day, it may cavitate and burn out prematurely unless you keep it primed with fluid. It may also be time-consuming to reinstall the pump and intake attachment at each use point. So, labor costs are also a factor.

Although the unit is available with a drum dolly, this dolly is only meant for ease of maneuverability when moving around your machine, such as during machine cleaning and recharge. A portable unit should be on a rugged frame for system protection, like on our Snapdragon™ Series. If your budget is limited, we also offer an air or electric diaphragm pump upgrade option for the Muscle unit.

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I like your Snapdragon Coalescer System, but I see that it has an air-powered pump. I would prefer to use it for a holding tank on the weekends, but my shop air is turned off then. Do you make it with an electric pump?

Yes, we do, and by popular demand! We can equip either of the Snapdragon models (the Deluxe or the ADAPT™) with this style pump upon request.

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I bought a different brand coalescer many years ago. Can your coalescing media work with it?

Yes. Our media can be added to any coalescing equipment and will improve their effectiveness. It increases the surface area in the holding tank to improve the separation time. It is a non consumable, and will never need replaced.

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How do I know if I should get mechanical skimmers or coalescers to remove tramp oils?

It is a matter of what best “fits” your application as well as your equipment preference.

More information on each product selection can be found in their product sections.

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What factors should I address when choosing the appropriate Muscle™ Coalescer?

The individual selection of a Muscle Coalescer depends upon application factors such as:

Chip removal requirements (removal of suspended and floating chips or swarf)
Metal chips chemically degrade coolant, so they are best removed, whenever possible. The smaller the chip size, the quicker this degradation takes place, so in grinding or cast iron machining, chip removal is definitely recommended. Choose the Deluxe w/Filter model whenever chip removal is of interest. Select the filter bag with a pore size relative to that of the chip size.
Type of coolant (full-synthetic, semi-synthetic or water-soluble oil)
For full synthetics, the Plus model is recommended. For semi-synthetics and water soluble oils, the Deluxe model is best due to the additional coalescing media which helps separate the tramp oil from the base oil.
Intake attachment selection will be based upon sump factors such as access to the area where installed, fluid level fluctuations, and surface debris.

A dedicated Muscle is best for each sump that sits idle more than one shift. Idle sumps biologically degrade more quickly than those that circulate. The Muscle will remove the tramp oils and also continuously aerate and circulate the sump, preventing bacterial rancidity.

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What factors should I address when choosing the appropriate Snapdragon™ Coalescer?

If you prefer one piece of equipment for use between various machines, you can choose a Snapdragon Portable Coalescer System, and then utilize an Oxygenator when the machine pumps are down to prevent coolant rancidity. See Oxygenator for details.

Drawbacks to the use of one piece of equipment are possible bacterial crosscontamination between sumps, required labor to move the unit daily between each sump, and minimal maintenance.

The individual selection of a Snapdragon depends upon application factors such as:

Chip removal requirements (removal of suspended and floating chips or swarf)
Both the Deluxe and the ADAPT filter the tramp oils from your coolant. Both have prepump filters to keep the pump healthy. But only the ADAPT will filter for small chips, and this ultra filtration is done after the oils are removed as to not re-emulsify the oil. This ultra filtration is recommended for applications where smooth surface finishes are required, such as burnishing or honing, or when tight tolerances, such as ± .0002”, need to be held.
Pressurization of the clean coolant return feed
Only the ADAPT model pumps the clean coolant back to your sump or other holding tank under pressure, so it does not have to be gravity-fed.
Overfill Prevention of the coalescing tank is supplied on the ADAPT model only
Coolant-free oil discharge is supplied only on the ADAPT model, as it comes equipped with the Internal Oil Discharge Skimmer, which collects the tramp oil in the coalescing tank for a more defined discharge of oil only.
Pulse Dampening is supplied only on the ADAPT model. This feature helps to relieve the “hammer effect” of the Hammerhead intake attachment (no pun intended). The Hammerhead has the potential to bounce on the fluid surface when in use with a diaphragm pump. This bounce can impede the oil draw process.
Intake attachment selection will be based upon sump factors such as access to the area where installed, fluid level fluctuations, and surface debris.

We recommend the Deluxe model if you do not require the additional features mentioned above. The ADAPT model, due to those features, will require additional operator training.