The pressure differential in the polyurethane foaming machine is too high. How can this be resolved?

During polyurethane foam and polyurea spray application, **excessive pressure imbalance in the spray machine** is one of the most common malfunctions.When the equipment detects that the pressure difference between the A and B sides exceeds the set value, it immediately triggers a pressure imbalance alarm; in severe cases, it will automatically stop spraying to prevent an imbalance in material ratios, which could affect construction quality. Excessive pressure imbalance not only reduces application efficiency but also leads to problems such as abnormal foam density, poor foaming results, and incomplete polyurea curing. Therefore, when the equipment triggers a pressure imbalance alarm, it is crucial to quickly identify the cause of the fault and resolve it promptly. From the perspective of the equipment’s operating principle, **there are essentially only two causes of excessive pressure differential:** - **Insufficient material supply on the side with lower pressure;** - **A blockage in the flow path on the high-pressure side, resulting in increased flow resistance.** Therefore, when troubleshooting pressure differential issues, it is essential to follow a systematic troubleshooting approach, using the simplest methods to quickly identify and resolve the problem. --- # Step 1: First, rule out booster pump failure Regardless of the brand of polyurethane spray machine—whether GRACO or PMC—when a pressure differential alarm occurs, it is recommended to first check whether the booster pump is operating normally. This is because the booster pump is responsible for continuously delivering raw material to the main unit; if internal leakage occurs in the booster pump, it will prevent that side from establishing stable pressure, thereby triggering a pressure differential alarm. ## How can you determine if the booster pump is leaking? The specific procedure is as follows: 1. Start the equipment and bring the pressures on both the A and B sides up to normal operating pressure. 2. Stop spraying, turn off the spray gun, and put the equipment into the "gun off, pressure maintained" state. 3. Observe the changes in the pressure gauges on the A and B sides. ### Determining the Result **Scenario 1: Pressure Remains Stable** If the pressures on both the A and B sides remain stable for an extended period without a noticeable drop, this indicates that the booster pump’s seals are functioning normally, and a booster pump malfunction can generally be ruled out. **Scenario 2: Pressure on one side continues to drop** If the pressure on one side continues to drop while the other side remains stable, this indicates an internal leak on the side where the pressure is dropping. Focus your inspection on the following components: - Booster pump packing - Booster pump piston seal - Check valve - Ball valve seal - Pressure Pump Repair Kit Wear or seal failure in any of the above components can cause material backflow, making it impossible to maintain stable pressure. Only after confirming that the booster pump is operating normally should you proceed to inspect other components; otherwise, subsequent troubleshooting may lead to misdiagnosis of the cause of the malfunction. --- # Step 2: Check the high-pressure side for blockages If the booster pump is operating normally but the equipment still triggers a pressure differential alarm, in most cases **there is a blockage on the side with higher pressure**. A blockage increases resistance to material flow, causing the pressure on that side to rise continuously and resulting in an imbalance between the pressures on sides A and B. ## First, check the spray gun The spray gun is the most common location for blockages and the most frequent cause of pressure differential alarms. Key areas to check: - Mix Chamber - Nozzle - Side Seal - Internal flow path of the spray gun If there is a small amount of cured material or impurities inside the spray gun, it will restrict the flow of material, causing the pressure on that side to rise significantly. We recommend replacing the mixing chamber or nozzle with new ones first for testing; this is the quickest way to verify the issue. --- ## Then check the heated hoses and piping If the spray gun is confirmed to be functioning normally, proceed to inspect the delivery system. Key points to check: - Whether the heated hose is clogged - Whether the JIC fittings are clogged - Are there any kinks in the tubing? - Are there any crystallizations or impurities inside the lines? - Is the fitting in front of the gun clogged? A blockage at any of these locations can cause pressure to rise, thereby triggering a differential pressure alarm. --- # Step 3: Check whether the feed system is supplying insufficient material If no blockage is found on the high-pressure side, check the feed system on the side with lower pressure. Insufficient feed prevents normal pressure from being established on that side, which is another major cause of differential pressure alarms. Focus on inspecting the following components: ## Feed pump Check whether the feed pump is operating normally and confirm that the feed is continuous and stable. If the feed pump is worn, the seals are damaged, or its suction capacity has decreased, this can result in insufficient feed. --- ## Feed filter A clogged filter directly affects the flow of raw material. Remove the filter screen to check for: - Solidified material - Impurities - Metal debris - Crystallized raw material If blockage is found, clean or replace the filter promptly. --- ## Suction tube Check the suction tube for: - Leaking air - Loose - Cracked - Drawing in air Air leaks in the suction hose can also cause insufficient material supply, leading to a drop in pressure. --- ## Raw Material Temperature When the raw material temperature is too low, viscosity increases significantly, leading to increased feeding resistance. Therefore, you should also verify: - whether the main unit’s heating temperature is normal; - Whether the temperature of the heating hoses is normal; - Whether the material drum temperature meets application requirements. --- # How can you prevent pressure differential alarms on the spray machine? To minimize pressure differential issues, it is recommended to perform regular maintenance on the equipment: - Thoroughly clean the spray gun at the end of each day’s work. - Clean or replace the feed filter regularly. - Regularly inspect the booster pump seals and check valves. - Check the suction hose for air leaks or signs of aging. - Maintain the material and equipment at the recommended application temperature. - Regularly inspect the heated hoses and all connections. - Use clean, compliant raw materials to prevent contaminants from entering the system. Good maintenance practices can effectively reduce the incidence of differential pressure alarms, extend equipment service life, and improve spraying efficiency. --- # Summary Excessive pressure differential in a spray machine is not an isolated fault but rather a symptom of abnormal equipment operation. From a working principle perspective, there are only two root causes: **insufficient material supply on the low-pressure side, or a blocked flow path on the high-pressure side.** During actual maintenance, always follow the troubleshooting approach of “**first inspect the booster pump, then check for blockages on the high-pressure side, and finally inspect the feed system on the low-pressure side**,” rather than blindly disassembling the equipment.Through a scientific fault diagnosis process, problems can be quickly pinpointed, repair time can be reduced, the operational stability of polyurethane and polyurea sprayers can be improved, and construction quality can be ensured.