Silo Protection Technical FAQ

Once you have connected your fill pipe, you will need to run a test of the silo protection system to make sure that all the safety equipment is functional and it is safe to fill. On the control panel, there will be either a push-button or turn-key marked GLT (Ground Level Test). If you require a key to operate the system but have not been given one, please speak to the site manager. Pushing the button/turning the key will activate the Ground Level Test, checking the silo safety equipment within approximately six seconds.

If everything is operating correctly, the SPS will open the butterfly valve at the fill point, and the screen on the control panel will inform you that it is safe to fill. The valve will remain open for 90 minutes, after which it will close, and you will be required to re-run the test if additional filling time is needed.

A pre-GLT failure is rare but not impossible. Firstly, ensure that there is a correct, functional power supply to the panel and that the panel is switched on. If you are competent to do so, check the 4 amp fuse which is on the left-hand side of the terminal rail in the panel. If the power supply is OK, try cycling the power to the panel to reset it. Check the compressed air supply is on and working correctly (correct pressure, no kinks or freezing of any moisture in the air pipe) and then rerun the test. 

If the panel is on and working correctly and it will still not run the GLT, then there is a pre-existing fault condition. Please check the panel screen for instructions and refer to the FAQ answers below.

DO NOT attempt to fill the silo without running an initial GLT.

To resolve this, inspect the pressure sensor. Doing so will require going to the silo-top if you are trained and competent; all appropriate safety procedures should be followed. The pressure sensor is an integrated component of several models of Hycontrol SPS, so you will have to refer to the manual to locate and remove it for inspection. Check the compressed air supply is working correctly (correct pressure, no kinks or freezing of any moisture in the air pipe). Check if there is any damage and that the end of the sensor (usually a white gauze) is clean and not blocked with the product.

Having done this, get a colleague to activate the GLT again. If the sensor passes the test this time, replace it and proceed normally. If it fails again or you can feel air coming out of the end of the sensor, then the solenoid is faulty. Inform the site manager and contact Hycontrol Technical Support.

This fault could be an issue with either the PRV itself or its proximity switch. Therefore, the pressure relief valve must be inspected. Doing this will require going to the silo-top, and so all appropriate safety procedures should be followed. Working at height should only be carried out by competent persons.

Remove the weather shield from the PRV and inspect it to see that it is clean and not clogged with product. Check that the PRV is not jammed open (use caution – do not put fingers inside the valve). Locate the proximity switch and check it is clean, is screwed in tightly on the lid, and the targeting plate (if used) is correctly located underneath it. When the valve is closed, there should be a 1-2 mm gap (approx) between the switch sensor and the target. There is an LED light on the top of the proximity switch which should glow solidly when closed. If the LED is not on this close to the target there is a fault and it may require replacing – inform site and contact Hycontrol.

Check that the valve opens and closes by pressing the yellow local test button located on the PRV electronics box. You are looking for the valve to open fully with a smooth movement – if the valve lid judders or gets stuck there may be an issue with the airline. Check the compressed air supply is working correctly (no kinks or freezing of any moisture in the air pipe) and the regulator on the PRV is set to 85 psi. If this does not resolve the issues, inform the site manager and contact Hycontrol Technical Support.

The silo may already be at capacity, so go to the top and (if possible) physically check the level inside. Note that, as always, working at height should only be carried out by competent persons. If the product has not reached the high-level, pull out the DP Series vibrating level probe, clean any accumulated product off it and check that it is functional. You should easily be able to hear/feel the probe vibrating, and be able to cause it to switch by holding the blade and muting the vibration with your hand – the relay switching should be an audible change. Once you have confirmed this, return the probe to the silo and rerun the GLT. As long as the probe is not making contact with the product surface, it should pass, and you can continue.

Note that in some instances, the sensitivity of the probe may need to be adjusted. For instructions on this, please refer to the DP Series manual.

If the probe does not switch, or if there is no vibration at all, then there is a fault which should be reported immediately.

The inlet valve WILL NOT OPEN if the GLT has failed, because the test routine has encountered an error with one of the vital silo safety devices and therefore attempting to fill the silo is not safe. DO NOT ATTEMPT TO FORCE THE VALVE OPEN.

The first thing to do is to check the panel. If the GLT has not failed, then it is likely to be a fault with the air supply to the butterfly valve itself. The valve is failsafe normally-closed, so a lack of compressed air will cause it to remain shut. Check the compressed air supply is working correctly (correct pressure, no kinks or freezing of any moisture in the air pipe) and rerun the test.

The inlet valve WILL NOT OPEN if the GLT has failed, because the test routine has encountered an error with one of the vital silo safety devices and therefore attempting to fill the silo is not safe. DO NOT ATTEMPT TO FORCE THE VALVE OPEN.

The first thing to do is to check the panel. The panel will tell you what alarm conditions are occurring and you can follow the on-screen instructions to take appropriate action to remedy it (if you are unsure what to do, refer to the individual alarm questions that follow in this FAQ).

If this is not the case, then it is likely to be a fault with the air supply to the butterfly valve itself. Refer to the question “Why won’t the inlet valve open?” above.

Repeat the test and see what the reported pressure on the screen is. If the pressure is below 40 millibars, there is an issue with the air supply. If it is above 40 millibars, there may be a blockage on the sensor. Therefore, you must inspect the pressure sensor. This test will require going to the silo-top, and so all appropriate safety procedures should be followed. Working at height should only be carried out by competent persons.

The pressure sensor is an integrated component of several models of Hycontrol SPS, so you will have to refer to the manual to locate and remove it for inspection. For a low-pressure issue, check the compressed air supply is working correctly. Make sure you are looking at the air regulator that feeds the pressure sensor NOT THE REGULATOR ON THE PRV. In freezing conditions, with poor site air supply, the pipes may be frozen, which will lead to a test fail.

For a high-pressure issue, check if there is any damage and that the end of the sensor (usually a white gauze) is clean and not blocked with the product. If the sensor is reporting a high pressure before delivery has been commenced, but there is no obvious damage or blockage of the sensor, high atmospheric pressure or weather conditions may be interfering with the site air regulator.

Having done this, get a colleague to activate the GLT again. If the sensor passes the test this time, replace it and proceed normally. If it fails again or you can feel air coming out of the end of the sensor, then the solenoid is faulty. Inform the site manager and contact Hycontrol Technical Support.

This could be an issue with either the PRV itself or its proximity switch. Therefore, you will need to inspect the pressure relief valve. Doing so will require going to the silo-top, and so all appropriate safety procedures should be followed. Working at height should only be carried out by competent persons.

Remove the weather shield from the PRV and inspect it to see that it is clean and not clogged with product. If the GLT has run, then the proximity switch should be functioning. Locate it and check it has not come loose during the test, is screwed in tightly on the lid, and the targeting plate (if used) is correctly positioned underneath it. When the valve is closed, there should be a 1-2 mm gap (approx) between the switch sensor and its target. There is an LED light on the top of the proximity switch which should glow when closed.

Check that the valve opens and closes by pressing the yellow local test button located on the PRV electronics box. CAUTION – do not put fingers inside the valve! You are looking for the lid to lift fully with a smooth opening movement – if the valve lid judders or gets stuck there may be an issue with the airline, so check the compressed air supply is working correctly. Set the air regulator on the PRV to 85 psi. If the air pressure is too low, the valve may not open to its full extent, which would result in a GLT failure. Check that this is correct and press the local test button again to check the valve fully opens smoothly.

If this does not resolve the issues, inform the site manager and contact Hycontrol Technical Support.

This alarm has occurred because something has triggered the silo protection system to defend the integrity of the vessel. Stop filling and refer to the screen on the control panel, which will tell you what alarm conditions are occurring. Follow the on-screen instructions to take appropriate action to remedy it (if you are unsure what to do, refer to the appropriate individual alarm questions in this FAQ).

After you have taken corrective action to remedy the alarm issue, rerun the GLT. If everything is okay, the test will pass, and the inlet valve will open again for 90 minutes. If another alarm occurs, please repeat this procedure.

A high-pressure alarm will have caused the inlet valve to close immediately. Make sure there is no flow from the tanker. Reset the system and rerun the GLT. If it passes and the valve re-opens, it is most likely that the blow-in pressure from the tanker was excessive and this caused the pressure in the silo to spike. Lower the pressure from the tanker to a safer level and continue to fill.

If the alarm keeps tripping and the pressure from the tanker is definitely at a safe level, this suggests that there is an issue with the silo filter/air vent unit that has restricted the airflow out of the vessel. This may occur more often when the fill is approaching the high level, and there is less airspace in the vessel. The filter on top of the silo must be inspected before filling continues. This inspection must be conducted by a competent person as it involves working at height. The cartridges on the filter must be checked and cleaned or replaced as required, and the air supply to the reverse jet cleaning system should be checked as well.

If you are using a low pressure for delivery and the filters are in good condition, but the pressure alarm continues to trip regularly, there may be a system error. Inform the site manager and contact Hycontrol Technical Support.

A high-level alarm will close the inlet valve after 30 seconds. If the level probe passed the GLT, then it is incredibly likely to be reporting the silo level correctly, and you have reached the maximum safe level.

If you do not believe this is the case, reset the system and rerun the GLT. If it passes as safe to fill, there may be an issue with the level probe wherein the sensitivity may need adjustment. In this case, or if there is level probe issue reported, refer to the FAQ answer “What if the panel says there is a high-level alarm before the GLT procedure?” above or contact Hycontrol Technical Support.

However, we must emphasise that it is probable that the high-level switch is reporting accurately. You may wish to consider installing a continuous level probe on your silo to provide accurate level readings at all times.

On most Hycontrol silo protection panels this is accessed by holding down the OK button. On the new SHIELD Lite system, access it by holding down the Mute button. The statistics reports will then cycle on the LED display screen.