By Jan Wienczkowski, Marketing Manager, General Equipment Company
What determines a strong attachment? The key component is compatibility, and it’s especially important in finding a good match to meet the digging requirements you have in front of you.
Much like the jobsites that pop up every year, there are plenty of variations of hole diggers on the market, not to mention the equipment they can be mounted on. Although it may seem like a simple pairing, hole digging attachments have multiple variables that need to be navigated before hooking up. The following are guidelines in determining what hole digger attachment to buy, rent and mount to achieve the highest productivity without risk of damage to your hole digger, your power source or yourself.
Power source
For attachable hydraulic units, hole diggers can operate from auxiliary hydraulic systems of mobile power sources including, skid steers, backhoes, industrial tractors, excavators and all-terrain forklifts.
There are five basic criteria to consider when matching hole digger attachments to your power source:
- The physical equipment fit
- The anticipated maximum auger diameter and digging depth
- Soil conditions
- Auxiliary hydraulic system rated flow settings
- Auxiliary hydraulic system rated pressure relief settings
Does the attachment fit?
All of the above criteria are important, but none of it will matter if the power source and lift height is not adequate to fit the hole digging equipment.
The maximum lift height from the ground to the bucket hinge pin must be at least high enough so the attached hole digger mounting frame, powerhead and auger (or auger and auger extension), clear the ground. This allows the rig to hang vertically plumb. From a safety perspective the attached hole digging rig must not exceed the tip or lift capacity of the power source at full height and extension of the lift arms.
In the same light, the power source must be of sufficient weight that it cannot be lifted off the ground as downforce is applied to the digging rig. Too light, and this will create a very unstable operating condition.
In determining if you have enough height from the hinge pin to the ground, understand the effective digging depth of an auger, or extension, is not the length of that piece of equipment.
As an example, the nominal, effective digging length of a 1-metre auger is from the tip of the boring head to the hub. The overall auger is longer than this dimension, and auger extensions have additional length built in too. Equipment can vary from manufacturer to manufacturer but know those inches add up.
As part of the overall setup, make sure the power source hydraulic hose lengths are long enough to reach the powerhead of the hole digger and handle the full range of motion required during operation to eliminate any unnecessary pinch points or abrasion. The hose and connector assemblies should conform to SAE standards such as 100R2 or 100R8 to provide adequate safety factors between system operating pressures and ultimate burst strengths.
While not all applications may allow for such a feature, such as attaching to a dipper stick, the hole digging equipment should have an anti-kickback device to prevent the rig from swinging toward or entering the cab while the power source is in motion.
Know your dig
What are your jobsite digging requirements? Knowing the diameter and depth of the holes, plus the type of soil on-site, impacts equipment choices as well as results. The soil density, whether it’s rocky, clay, hardpan, caliche, sand or something in-between determines the amount of resistance created during the digging process.
If working in softer soils, such as sandy loam, the job will typically generate less resistance to dig a hole than tougher soils, such as hardpan or caliche. However, both soft and hard soil types can be especially resistant to digging during periods of low moisture content.
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The power needed to dig a hole is directly proportional to the soil resistance encountered by the auger plus the diameter of the auger being used. With respect to the auger diameter, as you increase from one size to another, the increase in torque is not one-to-one, it’s exponential (soil resistance plus the square of the auger diameter). If not considered, your power source could be seriously underpowered for the exact same soil conditions and hole depth.
For example, a 30-cm-diameter auger requires four times the power of a 15-cm-diameter auger when used in the same soil conditions to achieve the same level of productivity. The auger diameter has only increased by a factor of two, but four times the digging torque will be required.
Some power sources may not be able to handle the additional auxiliary hydraulic operating system working pressure needed, which will result in a loss of productivity. To alleviate this, decrease the drilling rate of the larger auger, if possible, to fall back within the power source auxiliary hydraulic output capacity.
When factoring in the impacts of hole depth, keep in mind that as the auger string length (the auger plus any extensions) increases, torque requirements will increase.
Think of the auger string as a rope. As you add more auger extensions to the rope, each connection between components has some play in it to allow for installation and manufacturing tolerances. This play allows the rope to whip a little off centre as it rotates and, if the auger string becomes long enough, the hole will begin to wander and not be completely vertical. The combination of the whipping action and the off-vertical hole orientation can cause additional binding between the auger string and the hole. In some cases, the auger string can become stuck.
In the end, be especially mindful of the overall torque requirements needed to handle the resistance created by the soil types involved, coupled with the auger diameter and hole depth.
Find your attachment flow rate
You’ve determined a right-sized attachment for your power source and understand the job requirements at hand, but what about the hydraulic power being delivered and the amount the attachment can receive?
The auxiliary hydraulic system flow is rated in litres per minute. This is the amount of oil flow that can be produced by the hydraulic pump at a given engine speed. A general rule for flow rates is the higher the flow rate, the faster the auger will rotate.
Keep in mind the high end of the attachment flow rate is established for maximum powerhead motor efficiency and component life.
If the power source rate surpasses this maximum, the auxiliary system can be regulated with either engine speed or pump displacement depending on whether it is an open or closed centre hydraulic system, respectively. On the low end of the flow rate range or below, you use the same methods to prevent the auger from boring in like a screw and getting stuck or preventing the power source engine from stalling.
For viable power source equipment, look for a machine that lands in the litre per minute range required of your hole digger. The range can typically be found in the operator’s manual for the hole digger.
If the manual isn’t available, call the hole digger manufacturer for assistance to confirm the specific operating requirements.
Relief pressure
Next is the auxiliary hydraulic system rated pressure relief, which is measured in pounds per square inch (PSI) or kilograms per square centimetre (kg/cm2). This is the amount of pressure the hydraulic pump can produce before the system relief valve opens and bypasses the oil flow back to the reservoir. Basically, the higher the pressure relief valve setting, the greater amount of torque the hole digger will produce.
Like with the flow setting, you’ll want to match the rated pressure relief range from your power source’s manual to the hole digger’s range. In some scenarios, the auxiliary hydraulic system rated pressure relief may be higher than what’s ideal for the hole digger.
If this is true, the power source auxiliary hydraulic pressure relief valve setting needs to be set at full relief, and a dual inline relief valve between the auxiliary hydraulic system and the hole digger must be installed. If these adjustments are not made, you risk blowing out the seal of the motor in the hole digger powerhead and/or causing hydraulic hose failures. If the PSI value is too low, insufficient torque will be delivered to effectively dig the hole.
Now that you know your attachment flow rate and pressure relief rating, you can use these to determine the hydraulic horsepower of your power source and help fine-tune the power source selection to handle the work required. To do so, simply multiply the PSI rating by the litres per minute and then divide by 1,714.
Finally, be sure to scour the operator manuals of all equipment being considered for needed specifications and for operational safety guidelines. Leading manufacturers are eager to help, so call them, as some even offer 24-hour, toll-free phone support that can answer questions quicker or better than a manual. Making the right choice is important, so don’t throw caution to the wind.
Do the due diligence and get the job done right with no regrets.
