Knowledge Center
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Accumulator Systems
PDF File of Accumulator Systems
Holland Dollies can be used in a system to carry a load completely or they can be used in conjunction with other transport systems with the use of accumulators. Often, the Department of Transportation will require dollies in conjunction with heavy transport trailers crossing bridges. By adding the Holland Dollie with accumulators, the load is distributed over a larger area.
Pictures from a 3-D model illustrate the basic idea behind the system. The Holland Dollie must be able to apply force to the load in some manner in order to take weight. For illustration purposes, we have shown the dolly pushing on a beam under the load. This could be achieved many different ways, but for simplicity we have used a beam under the load.
Through the hydraulic cylinder a calculated portion of the load is applied to the dolly by specifying the correct hydraulic pressure. This can be calculated or looked up in a table provided by Holland Moving & Rigging Supplies. The table converts the hydraulic pressure in the dolly cylinder to weight it is carrying. When the dolly cylinder is connected to the accumulator, it will allow the dolly to travel up and down and to adjust to the differences in height between the trailer and dolly. The figure below shows the initial starting conditions of the accumulator and dolly cylinder. More about this will be discussed later.
The picture below shows a total of four dollies under the load. Steering can be accomplished by mechanically tying the tongue of the dollies to the load. In this case, the dollies act similar to another straight axle under the load. Turning corners with the dollies down may require caster steering. With caster steering, the dollies will follow the load around the corner. To visualize this, one can think of a shopping cart caster.
An accumulator charged with nitrogen acts like a spring when connected to hydraulic circuit with the dolly cylinder. As illustrated below, the accumulator will displace oil to the dolly cylinder if the dolly encounters a dip in the road. Under the opposite circumstances, the accumulator will accept oil displaced by the dolly cylinder when the dolly travels over a rise in the road. All of this acts to maintain a relatively constant weight on the Holland Dollie.
For traveling long distances where the dollies are not needed to take weight, they can be pulled up. The cylinder in the Holland Dollie is double acting, which allows you to lift the dolly up off the ground. In the picture below, the dollies would be pulled up to the cross beams. Then the dollies would be tied securely so they would not swivel or rock. This allows the load to travel down the road without pulling the dollies off of the load.
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Bolster Bolt
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Building Move - Steel
Ron Holland Housemoving, Inc. moved a 40 ft by 155 ft building for Pioneer Seeds in the fall of 2008. The building was moved approximately 300 feet on site in order to make room for a new facility. Wet fall weather made scheduling and moving more difficult. Pioneer was very accommodating allowing Ron Holland Housemoving to work after hours bringing in equipment and on weekends to obtain the best moving conditions.
Even with re-scheduling for moving on the weekend, the route was still a bit slippery. Holland Power Dollies were used to help overcome some of the more difficult ground conditions and to push the rear of the building. The building was moved across an empty corn field with light snow on the ground. As the day progressed, the snow began to melt creating slippery conditions for the move. The limited slip traction of the Holland Power Dollies was definitely an asset on this move.
The building was a large steel structure weighing 33 tons. Each main beam used to support the building’s frame consisted of three pieces of steel, 94 ft + 33 ft + 28 ft, which were bolted together to make the 155 ft main beam weighing in at 144 lb/ft. All seven cross beams were bar clamped with 1 ¼ inch bolts to the main beams. The total weight of the steel and building was 70 tons.
The above figure shows how the move was engineered. Cross beams were placed at 25' intervals with jacking points as indicated. A unified jacking system lifted the structure using 8 jacks. The unified jacking system allowed the moving foreman, Art Schulz, to lift the building evenly to a position where the dollies could be placed under the load.
Holland Plate Dollies were placed in the forward position behind the truck while Holland Power Dollies were placed at the rear of the building 50 ft from the caster plate dollies. The power unit to run the Holland Power Dollies was positioned on the main beams.
The move began with the truck pulling out onto the snow covered field and the power dollies pushing the rear. The field was very uneven at times; however, since the building was loaded on a three-point system the structure remained in a level plane. As the dollies traversed the dips in the field, the hydraulic cylinders in the dollies adjusted for the uneven ground to prevent the building from bending or twisting. Once the movers had negotiated the snow covered field, the building was pushed up onto the new concrete foundation completing another successful move.
This information is provided as our experience and is not meant to be used as a recommendation for steel placement in other projects. It is very important that a structural analysis is completed on every structure that is moved.
- Crib Jack Specifications
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Holland Dollie 3-Point Loading
The cylinders of all the Holland Dollies in a transport system must be connected to maintain a 3 point loading system for the object being moved. Maintaining a 3 point loading system allows the dollies to move over uneven ground without causing any damage to the structure or object being moved. The structure or object may tilt in one direction or another, but will remain in a single plane. In the case of a truck and dolly system, the truck is one point. If the dollies are positioned on either side of the center line of the structure or object, then all of the dollies along one side have their cylinders hydraulically plumbed to the same source. Each set of dollies creates a point in the hydraulic system giving points 2 and 3.
If a single dolly on one side encounters a rise in the road, then the pressure in that cylinder increases and immediately forces the hydraulic fluid to the other cylinders in the same zone. The stroke of the dolly encountering the obstacle reduces and the stroke of the cylinders of the other dollies in the same zone increases as the pressure of the hydraulic fluid is evened out. The hydraulic system maintains a single plane.
The dolly also has an oscillating top cap and top plate in order to evenly distribute the load. Each cylinder in a dolly is attached to an oscillating top cap connected to a top plate. The load is directed onto the top plate. As the dolly encounters obstacles in the road, the top plate oscillates to maintain contact and continue even distribution of the load to all the dollies. Each dolly axle also oscillates under the load in order to maintain even contact and pressure on the road.
- Plate Dollie Dimensions
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Power Dollie Freewheeling
Freewheeling Holland Power Dollie pdf
Holland Moving & Rigging Supplies utilizes a unique drive system on it’s freewheeling Holland Power Dollies. The drive is comprised of a radial piston motor that pushes on a cam ring causing the housing to rotate. The motor has several advantages.
Feature: The motors run smoothly at speeds close to zero.
Benefit: This translates to fine control to precisely move your loads at low speed.
Feature: High starting torque.
Benefit: Starting from a standstill, you have large torque available to move the load. Some types of motors only have significant torque after they have started moving.
Feature: Mechanically freewheeling.
Benefit: Hydraulic power is not required to freewheel the motor. The motor is also capable of freewheeling at significant speeds. In addition, there is no oil shear. A gearbox drive will build up heat due to the large gear reductions used.
The mechanical freewheeling feature of the Holland Power Dollie is unique and a significant benefit when traveling over the road. The Power Dollie can be used on site in drive mode to move the load and then be placed in freewheeling mode to travel on the road. Without this feature, the dolly would have to be swapped out with a different dolly to travel down the road. This process would have to be reversed when arriving at the new location.
The hydraulic motor used in the Holland Power Dollie can freewheel at rpms in excess of 600 rpm. When using 22.5 tires at 600 rpm the dolly can reach a freewheeling speed of approximately 66 mph. Unlike a gearbox drive, the hydraulic motor in a Holland Power Dollie will not build up heat due to oil shear of the gears and will not be limited to very low speeds while freewheeling. The hydraulic motor in a Holland Power Dollie is capable of freewheeling faster than the dolly can be used in most situations.
The Holland Power Dollie’s freewheeling capability provides superior versatility over other competitor’s solutions.
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Power Dollie Limited Slip vs Positraction
The Powered Holland Dollie has a drive system capable of limited slip on the rear axle. This means that if one wheel is in slippery conditions, then the drive will engage the other wheel on the axle and continue forward movement of the dolly and load. The engagement of the limited slip is automatic. The point at which the limited slip activates can be adjusted by changing the orifice size on the drive. It is not necessary to set a switch. When the limited slip is not required, then the drive runs without engaging. The limited slip feature allows for easier steering than with positraction.
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Power Dollie Safety Valve
Every Holland Power Dollie features a safety holding valve that automatically closes if a drive hose breaks. This action takes place faster than the operator can react manually and prevents a run away condition.
The manifold also has a pressure relief valve on the case drain to protect the case seals of the hydraulic motor. The relief valve will prevent accidental case over pressurization and costly down time.
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Rental
Do you need extra dollies for a move? Not a problem.
Holland Moving & Rigging Supplies has Holland Plate Dollies, Holland Air Dollies, Holland Power Dollies and Holland Power Units available for rental to expand your moving capabilities.
Dollies can be rented on a month to month basis.
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Steering Holland Dollies
Holland Dollies: Caster (Auto) Steering, Power Steering & Electronic Steering
Dollies can be steered directly with hydraulic power steering, mechanically steered or steering can even be controlled electronically. When a dolly is placed in caster mode or auto steering, it is able to move freely with the load and compensate for turns without being steered directly.
In the first example in the video a Holland Power Dollie is hydraulically steering the front of a kiln section that was removed from a cement plant. The tongues of the dollies are connected and the single dolly controls the direction of both front dollies. The rear set of dollies in this case are being mechanically driven. If the rear set of dollies also had power steering, then the entire system could be driven and steered with a single remote control.
In the second example in the video there are 3 sets of dollies under a long building being moved with a truck on the front of the load. The first set of dollies have an evener connecting the tongues and are in caster mode to follow the movement of the truck. The middle set of dollies have their tongues connected via an evener bar. These dollies happen to be Power Holland Dollies. They are actively hydraulically steered and driven in order to move the rear of the long building through a 180 degree turn. The third set of dollies are set in caster mode, but they do not have the dolly tongues connected. You can see that the third set of dollies caster a great deal in order to follow the load.
The 150 ton dolly modules were designed to electronically steer. This system also was designed with load tracking capability. While the front module was electronically steered, the rear module automatically sensed were the load was and adjusted accordingly. Load tracking is very advantageous allowing the remote control operator to safely drive the entire load by steering only the front module.
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