What a High-Shear Bentonite Mixer Does, and How to Tell Your Mud Is Fully Yielded

By Stuart Allan, Surface To Surface Inc.

If you’ve ever cleaned lumps off a screen, or watched viscosity keep climbing an hour after you thought the batch was done, you know the difference between mud that’s mixed and mud that’s yielded. A bentonite mixer’s whole job is to close that gap fast, so the rig isn’t waiting on you.

What high shear does to bentonite

Bentonite is a clay. Dry, it’s a powder of fine particles. To build viscosity and gel, each particle has to get wet, take on water, swell and separate from the ones around it. That’s yield. Until then, you’re paying for bentonite that isn’t working.

The trouble starts in the first second. Dump dry bentonite into slow-moving water and the outside of each clump wets and swells into a skin. That skin keeps water out of the middle. Now you have fish eyes: gel balls with dry powder inside. Stirring won’t break them. They ride around the tank, plug screens and nozzles, and the powder inside is wasted.

High shear fixes that by hitting the powder with fast-moving fluid the moment it gets wet, tearing it apart before a skin can form. That’s where mixing speed comes from. Our M-375 takes a batch to fully sheared fluid in under 5 minutes, and the M-750 makes 750 gallons of fully yielded mud in under 8.

How the hopper, nozzle and shear work

Every STS mixer runs the same basic loop, and it’s what you troubleshoot on the job.

The pump pulls from the tank and pushes fluid into the mixing tee.

The jetting nozzle in the tee squeezes that flow down to a small bore: about 11/16″ on our 2″ and 3″ systems, and 1″ on our 4″ systems. The 2″, 3″ or 4″ is the pipe size of the system, not the hole the fluid goes through.

The hopper sits over the tee. The jet coming out of the nozzle pulls bentonite or polymer down out of the hopper and into the stream.

The shear happens right there. Dry product meets a fast jet and gets torn apart as it’s wetted. Mixed fluid goes back to the tank, the tank jets keep the whole tank rolling, and it all comes around through the pump again. We call it a four-point system because mixing, shearing, agitation and delivery all run through one design.

You don’t need to close the jet guns to check the gauge. Running with the guns open, about 30 to 35 psi is normal. Opening or closing the guns changes the reading: close them and all the flow goes through the mix nozzle, so the pressure goes up. With the guns closed at about 42 psi, a 2″ or 3″ nozzle moves roughly 87 GPM through the hopper and a 4″ about 184. Those are calculated clean-water figures, not mud. For the full breakdown, see Hopper Nozzle GPM: Reading Your Mud Mixer Gauge.

How to tell your mud is fully yielded

• Look at it. Pull a bucket off the discharge. Lumps, fish eyes or a grainy feel mean it isn’t there yet.
• Check it twice. Run a Marsh funnel, let the tank circulate, then run it again. If the number is still climbing, the mud was still yielding when you started pumping it.
• Feed the hopper steadily. Pouring faster than the jet can take it is the usual cause of fish eyes. The M2 hopper holds half a bag, which helps pace it.
• Watch the gauge over time. A new machine reads at spec. Write down your baseline, guns open and guns closed, while the unit is new. If the reading falls over time, the impeller may be wearing or something else in the system is giving. That’s the telltale sign that pressure is dropping, and the efficiency of the whole system with it. Check the impeller, the nozzle and the suction side before you blame the bentonite.
• Follow your mud supplier’s mix sheet for water treatment and for the order you add bentonite and polymer.
• Clean up after the job. Bentonite left to sit sets up hard. Use the hopper wash wand.

Choosing a size

Size the mixer to how fast your rig uses mud, not to the biggest tank you can haul. A smaller tank that yields fast can keep up better than a big one that yields slow.

Keep your pump and tank, add our hopper. The M2-850 2″ High Shear Hopper System connects to your pump and tank with cam locks. The manifold has one valve for agitation and one for supply to the drill, and it comes with a wash wand. It’s a hopper add-on, not a mixer. It runs off your pump.

Mixer only, on your tank. The M2, M3 and M4 are compact units with 2″, 3″ and 4″ pumps. The M2 comes with eductor nozzles to install in your tank, or you can pair it with our UTK-500 tank.

Complete system. Tank, pump and mixing system together:

The M-375 and M-500 are built for mini HDD rigs and tunnelers. The M-500 also comes as a tank-and-mixer combination: our UTK-500 with an M2 or M3. The M-750 comes in the original square layout or a longer, narrower version for tight sites. The M-1500 can mix 750 gallons while holding 750 gallons of water in reserve.

If you’re between sizes, call us with your rig, your typical bore and how much mud you go through in a shift. For a side-by-side checklist, see our HDD mud mixer buyer’s guide, or compare every unit on the mixing systems page.

Agitating and supplying at the same time

If a mixer has to stop agitating to feed the rig, solids settle. If it stops feeding to agitate, the rig waits. On our units it depends on the model and the plumbing:

• The M2-850 has separate agitation and supply valves on the manifold.
• The M-750 can draw water from a second tank and send mud to the rig or a storage tank without a second pump.
• The M-1500 has the option of a second pump to supply the drill and mix top-up batches without stopping production.

For the others, ask us how it’ll be set up on your job.

Power options

The units in our webstore are gas. Diesel and electric versions of the M2, M3, M4, M-375, M-500, M-750 and M-1500 are built to order. For those, ask us for a quote.

Core drilling and underground: when a MAC unit fits

Mineral exploration and underground core drilling is a different problem: water and additive are expensive to get to the rig, so you want to reuse your returns. That’s what the MAC JR-1200 and MINI MAC 950 are for. They’re mix-clean-recover units, not HDD mixers.

Each one is built around an STS M2 mixer with three tanks and two 2-1/2″ hydrocyclones. You mix new fluid in the mix tank and send it to the active tank that feeds the rig. Your pit pump fills the center “dirty” tank with returns. The mixer’s pump runs that fluid through the hydrocyclones, and the clean overflow goes back to the active tank. One motor and one pump do all of it.

Both run from ground level. The MAC JR-1200 is on wheels and rests on the ground when it’s working. The MINI MAC 950 is on a skid, with a smaller footprint. The spec sheets show electric models, with diesel versions available. Both are priced by quote.

If you’re drilling HDD, you don’t need a MAC.

Talk to us

Not sure which unit fits your rig? Call 800-567-0978 or request a quote.