Using spray foam insulation is a widely accepted method of insulating residential and commercial properties. Spray foam provides superior insulation, meets the demand for homes and buildings to be more energy efficient, and complies with new building codes requiring tighter, more energy efficient standards.
Spray foam is made by combining two liquid chemicals; an isocyanate (A) and a polyol resin (B). Once these chemicals are mixed, they are sprayed onto a substrate. Mixing these two chemicals creates an instantaneous chemical reaction.
The two liquids, when mixed quickly, typically expand between 10-50 times in size and fully cure to the touch within a few seconds, resulting in the final spray foam product.
Spray foam is manufactured on-site at the time of application, whereas most other building products – such as drywall, fiberglass insulation, oriented strand board (osb), roof tiles, lumber and duct work – are manufactured in a factory and delivered to the job site.
This allows for the materials to be spray applied as a liquid, allowing it to better insulate by completely expanding to fill gaps, cavities, around pipes, wires, in tight spaces, etc. Since it is manufactured on-site, having the proper controls in place to ensure it is manufactured correctly is important.
Choice of the Right Equipment is Vital
The equipment needed to correctly mix and spray these chemicals must have the ability to heat and pressurize the materials. It must also have a robust mixing method that ensures a homogenous mix. Properly mixing two components on-site requires professional equipment.
Most spray foam chemistries today require a 1:1 ratio to mix properly and obtain the optimal properties the material manufacturers design their chemistries to achieve. When applied correctly, spray foam offers many benefits, but if misapplied, may cause issues that become difficult and expensive to remedy.
The best course of action is to prevent issues from occurring. Therefore, relying on the installer alone to make sure the foam is being properly manufactured may no longer be adequate.
As more builders are adopting the use of spray foam in their homes and more homeowners become educated in spray foam, they are looking for assurances that the spray foam application in their homes was done correctly.
This is where having spray foam equipment that is designed to mitigate the risk of spraying “bad foam” is important. Not only should the system have the capability of detecting possible issues with the equipment, process and chemicals, it should also save and provide the data in a usable format should customers request this information.
Graco’s spray foam equipment is designed to diminish potential issues with a robust design and software that monitors and controls pressures and temperatures. It is also designed to alert the operator and shut down the machine if potential issues are detected.
Although Graco equipment is designed to help prevent spraying “bad foam” by detecting potential equipment issues, many of the bad foam related issues are not due to equipment problems but rather factors that are under the control of the insulation contractor: such as improperly conditioned chemical or using a mix chamber which is too large for their feed system.
The equipment is also mechanical and will require preventive maintenance over time and may experience issues that require repair. For all these reasons, having equipment that can detect potential off-ratio issues is important.
What are Single-Point Variables?
It is important to understand the types of issues that may cause off-ratio foam to be sprayed. These types
of issues are called single-point variables, and can fall into several categories:
• Air in the fluid stream,
• An undersized feed pump,
• Poor material feed to the proportioner,
• Proportioner pump issues,
• Fluid leaks,
• Fluid restriction in heated hose or spray gun.
Through understanding these different single-point variables, detection methods can be designed for each one. Once the variable type is detected, it can be monitored.
The goal is to monitor for each of these variables and shut the proportioner down if one is detected, thereby preventing off-ratio foam from being sprayed. The operator can then make the necessary updates or perform the necessary maintenance to eliminate the issue causing the off-ratio condition.
Graco’s Ratio Assurance System
No single method can easily and accurately detect each of the potential single-point variables. A robust ratio control system must be multi-tiered and have more than just flow meters.
The foundation of the system starts with mechanically linked pumps and then adds positive displacement piston pumps, pressure monitoring, and flow meters to provide a ratio assurance system with built-in redundancies that will provide unsurpassed results in detecting off-ratio conditions.
Mechanically Linked Pumps
The core of every Graco Reactor is mechanically linked pumps, which covers the pumps on all electric, hydraulic, and pneumatic Reactors. The term “mechanically linked pumps” simply means that both the A and B pumps are connected together either by a shaft or a yoke so that both pumps stroke evenly at the same rate.
By mechanically linking the pumps each time the A pump is cycled the B pump must also cycle. This forces the pumps to cycle evenly and equally, resulting in the pumps pumping on-ratio.
Graco has always believed that mechanically linking the A and B pumps provides a robust system designed for 1:1 ratio spraying. In a sense, mechanically linked pumps are like built-in flow meters, in that the pumps naturally dispense equal amounts of A and B chemicals at each stroke.
Since the ratio is fixed, mechanically linked pumps provide a consistent ratio in a tight tolerance band. Mechanically linked pumps are also not dependent on flow meters to pump on-ratio. A mechanically linked pump is designed to automatically pump equal volumes of both A and B materials.
Positive Displacement Piston Pumps
The type of pumps used for spray foam and coating applications is also important. The positive displacement piston pump is a proven design that Graco believes is the best type of pump for this application.
A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. Positive displacement piston pumps provide consistent volumetric performance over a large range of temperatures, pressures and thus viscosities.
Piston pumps are more accurate for use in start and stop applications and for maintaining a stall pressure. Piston pumps can maintain accurate volume per cycle over long periods of use even with aggressive fluids.
Graco’s piston pumps are precision machined using state-of-the-art CNC machining equipment and are held to very tight tolerances assuring consistency from pump to pump. This is important when depending on two pumps in a system for equal volumes of material. Graco’s tolerance between pumps is held to less than 1%.
Inlet Pressure Monitoring
Monitoring changes in inlet pressure is a quick and reliable way to detect potential feed pump and material feed issues that could cause off-ratio material. Inlet pressure monitoring is a standard feature on Graco’s Reactor 2 elite models.
By monitoring when the inlet pressure falls below an acceptable pressure a problem can be detected and the user alerted. Although flow meters and outlet pressure monitoring may also be able to detect feed related issues, inlet pressure monitoring is the most accurate and quickest responding method of detection.
Some of the most common issues include running out of chemicals, cold chemicals, or the feed pump(s) being undersized for the required demand; these are all best detected using inlet pressure monitoring.a
Outlet Pressure Monitoring
Outlet pressure monitoring is standard on all electric and hydraulic reactors. Graco has always used the pressure differential between the A and B chemicals as a way to detect and prevent off-ratio spraying.
Reactors have a pressure differential alarm default setting of 35 Bar (customers have the option of changing this value to best suit their needs). Once the pressure differential between the A and B chemicals exceeds 35 Bar the Reactor will shut down.
Using pressure monitoring has always been the way to detect the majority of off-ratio conditions. Although this rule of thumb works in most cases, there are exceptions to the rule. Outlet pressure monitoring can also help detect conditions that may cause poor impingement mixing of the A and B chemicals.
Poor impingement mixing may occur even when chemicals are on-ratio. Possible causes of impingement mix issues include a clogged gun filter and/or clogged impingement port(s) in the side seals of the gun.
These types of issues will cause the pressure of one of the chemicals to increase, thereby affecting impingement mixing. As the pressure differential between the A and B chemicals gets larger, complete impingement mixing becomes more difficult.
Outlet pressure monitoring can detect these types of issues when the pressure differential exceeds the alarm threshold and will shut down the machine in an attempt to prevent improperly mixed materials from being dispensed.
Flow Meters
Flow meters can detect certain conditions that may cause off-ratio dispensing that may not be detected using inlet or outlet pressure monitoring alone. Flow meters are best at detecting issues related to the proportioner pumps, air in the feed lines/system and some fluid leaks.
Adding flow meters to the strong Reactor foundation of mechanically linked positive displacement piston pumps and inlet and outlet pressure monitoring provides an additional level of ratio assurance protection to the system.
Flow meters tie the complete system together with the ability to measure, monitor, and record true volumes of the A and B materials. By knowing the true volumes dispensed, this data can be made available to the customer. The Graco Reactor 2 ratio assurance system uses oval gear flow meters.
Oval gear flow meters have a number of advantages including cost effectiveness, accuracy, ease of installation, and versatility. Oval gear flow meters are generally regarded as one of the more cost-effective options for liquid flow measurement.
This type of flow meter is ideally suited for measurement of fluids having a range of viscosities and high flow rates. The gear meters used with Reactor, once factory calibrated, have an accuracy of ±1%. Ease of installation is another advantage of the oval design.
Because no straight pipe runs or flow conditioning are required, oval gear meters can be installed in tight areas where alternative technologies would fail.
Oval gear flow meters are also an excellent choice for any number of industrial applications including chemicals, petrochemicals, water, oils, diesel fuel, paints, coatings, greases, and solvents. Oval gear flow meters are by design simple and robust.
Two interlocking oval shaped gears offset by 90 degrees rotate within a chamber of known volume.
As these gears turn, they repeatedly fill and empty a very precise volume of fluid between the outer oval shape of the gears and the inner chamber walls. Each complete 180-degree rotation of the gears is called a pulse. The flow rate is then calculated based on the number of pulses recorded.
Tom Vandevenne – Ürün Satış Uzmanı – Product Marketing Specialist – Graco
