Rescue tools: Speed versus control
This article aims to provide more information about use of the flow control mechanism in hydraulic rescue tools to regulate the speed of operation. A good understanding of this feature will help you to perform extrications in the quickest and safest possible way. We will also look at the differences between conventional hose tools and battery tools.
Flow Control Conventional Tools
In the past, the rescue service only worked with conventional external pump driven rescue tools, i.e. “corded tools”, using a length of hose to deliver power to the tool. When rescuers were trained, we promoted constant activation of the control mechanism, whether it be thumb control, dead man grip or some other type of valve activator. The reason being, with a hosed system, any release of the control diverted flow from the piston in the tool and relieved pressure in the line. When the control was reactivated, it could take several seconds to rebuild pressure in the line depending on the length of hose being used.
Holding and Rebuilding Pressure
Every modern hydraulic rescue tool, regardless of brand or manufacturer and regardless of being battery driven or powered by an external pump, utilizes a dual pilot check valve in the system. This device holds pressure inside the tool when the oil flow is diverted. It allows a tool to hold a load or maintain a grip when there is no flow from the pump. The only way to release cylinder pressure is to open the check valve with flow through the control mechanism. This is not a new or exclusive feature. Why then does it take time to rebuild pressure in conventional “corded tools” ?
Pressure Building Delay
This is because of volumetric expansion of the hydraulic hose. The hose expands as pressure builds. This delays the time that pressure builds inside the cylinder creating power in the tool. If an operator stops repeatedly in an operation, the time to complete a simple hinge spread can be extended greatly. This is characteristic of any hosed rescue system, regardless of manufacturer.
Less Delay with Core Hose
Holmatro dramatically reduced the time to rebuild pressure with the CORE (coaxial) hose technology they introduced back in 2005. Due to the construction of the CORE hose, volumetric expansion is less than that of conventional twin line hoses. However, there was still an inevitable delay.
Flow Control Battery Tools
Move forward now to present day and the widespread use of battery driven rescue tools, the game has changed a bit. Battery powered rescue tools are for the most part self-contained. The motor, pump, oil reservoir and hydraulic cylinders are constructed as one unit. Most manufacturers use little or no fluid conductors to move oil from the pump to the cylinder. There is a direct connection and pressure builds almost immediately. This is universal amongst manufacturers and can be a big advantage if it is necessary to stop an operation for safety reasons.
Avoid Jerky Movements
However, constant stopping and starting of a cutting or spreading operation, even with battery tools, can adversely affect the outcome. Obviously it creates jerky movements that can make it hard to control tool reaction. This sudden tool movement can be dangerous and can lead to further injury to a patient or injury to an operator.
During a cut on today’s hardened steels, the steel absorbs energy from the tool until it reaches the point that it fractures. Stopping and starting can allow energy to dissipate and increase the overall time needed to make the cut. Stopping and restarting a spreader can again allow energy to be absorbed and sheet metal to fail instead of hinges. This leads to ripped metal and delays the desired outcome. Power must be controlled and applied in a steady, constant manner to be most efficient and most effective.
Precise Speed Control: "Feathering"
Holmatro has done this by allowing the operator to control the speed of the tool very precisely with their dead man control handle, which applies even more so to the new and improved version on their 5000 series of CORE tools: Flow can be controlled regulating the speed of cylinder movement, while still providing the full range of pressure to create power.
Speed Control in EVO 3 Tools
The control handle on Holmatro’s EVO 3 battery tools also offers precise speed control. It enables fast and efficient opening and closing of tools for positioning or for quick cuts and spreads. However, during very technical operations, when working in close proximity to a patient or when working in tight spaces where tool reaction can cause safety issues, the operator needs to have ultimate control. In this situation, the tool can be utilized as required, i.e. in a slow and precise manner, without jerky movements.
Performing an extrication is all about finding the right balance between speed and control. You want to get your patient out of that car as quickly and as safely as possible. Understanding the flow control mechanism and pressure building in both battery tools and conventional hose tools will help you achieve the most favorable result.
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