Woodward SOGAV 250 solenoid valve drives gas intake valve for troubleshooting

Woodward SOGAV 250 solenoid valve drives gas intake valve for troubleshooting

First identify the fault area, do not dismantle the valve first

Woodward SOGAV 250 is an electronically controlled gas intake valve that relies on an E-core electromagnet to generate magnetic force, attracting a low low carbon steel armature connected to the valve mechanism, allowing the valve to quickly open and close within a short stroke of approximately 0.50 mm. The valve body adopts a multi concentric groove surface sealing structure, and the dynamic metering plate presses the lower stop metering plate under the unbalanced action of spring force and pressure, forming overlapping and ground sealing surfaces when closed; When powered on, the moving plate is pulled apart, and the gas flows from the driven plate groove to the lower stop plate groove. Its advantages are short stroke, high force, and fast response, so on-site faults cannot only focus on the "valve body", but should be investigated separately according to the four domains of electrical, mechanical, pneumatic, and control timing.

Sogav 250 has unbalanced bottom load and unbalanced top load versions, as well as balanced top load versions. The structure and replacement parts cannot be mixed. The gas outlet seat ring of the bottom load version should be flush with the valve housing surface after installation, which is crucial in subsequent stroke inspections. Any disassembly should be carried out after cutting off power, gas, and confirming that there is no pressure; Unauthorized disassembly may also affect warranty.

Installation quality determines half of the faults

Before installation, it is necessary to ensure absolute cleanliness inside the gas manifold, without dust, welding slag, or metal shavings. Pollutants can get stuck between the measuring plates, causing internal leakage, insufficient travel, or valve failure, and in severe cases, enter the engine. The area around the installation base should also be cleaned to prevent debris from falling into the air manifold during installation.

Select the correct O-ring according to the outline drawing and install it into the valve seat groove; Secure the valve to the cylinder head or intake manifold using M10 or 3/8-inch hex socket screws. Use hex socket to avoid bolt head space and tighten evenly to the recommended torque by the engine manufacturer. The gas intake pipe is equipped with M8 × 1.25 screws, with at least 10 teeth engaged. After lubricating the threads, tighten them evenly to 20 N · m. The cable joint should be installed at the end, and the roller lock nut should be tightened; The coil grounding terminal must be reliably grounded.

Sogav 250 does not have on-site adjustable items. After installation, first pressurize the gas manifold with air or inert gas, and check all valves and interface flanges for leaks with soapy water. When the background noise is low, basic movements can be determined by listening to the "ticking" sound. The installation direction of the valve body should be vertical, with the inlet facing upwards and the electromagnet higher than the measuring plate; Horizontal installation will significantly shorten the lifespan. Valves and wiring harnesses should be kept away from extremely hot surfaces such as exhaust.

In terms of application layout, the valve should be placed as close as possible to the intake valve, shortening the connection channel from the valve to the intake manifold; The inner diameter of the gas supply pipe shall not be smaller than the valve inlet hole, and the valve inlet diameter shall be about 94-96mm. The shorter the pipe, the better. All gas supply pipes should be of equal length to avoid differences in intake between cylinders. The opening of the installation surface should be between 95-110mm. If it is too small, the flow rate should be limited, and if it is too large, the lower plate cannot be properly pressed. The gas supply pipe should not apply significant stress to the valve body, and flexible pipes should be preferred over rigid welded components. The gas manifold should be large enough, preferably with multiple gas supply points, to avoid remote valve starvation due to pressure drop when multiple valves are opened simultaneously.

Electrical drive and wiring harness are high-frequency fault points

The Sogav 250 must be provided with a dedicated current limiting driver to provide a periodic two segment current waveform: the first segment is a larger pull in current, and the second segment is a smaller hold current. The maximum values of input current and input power on the coil nameplate cannot exceed, otherwise it will exceed the allowable temperature rise at the highest ambient temperature. To determine whether two waveforms are suitable, equivalent average DC EADC and equivalent average power EAP should be used, rather than just looking at peak current; The worst-case scenario is the waveform with the highest duty cycle. EAP can be estimated based on EADC ² × Rc, where Rc is taken as the coil resistance at the highest rated temperature.

In terms of wiring, the cable from the In Pulse unit to the valve should be a shielded dual core wire, with the shielding layer grounded at the In Pulse connector end and the valve end not grounded. When using Woodward In Pulse II or ECM3 controllers, Sogav cable shielding should not be grounded at the valve end, and cable joints should be selected as non grounded type; Otherwise, it may cause operational issues with the controller and engine, and render the controller's EMC certification invalid. Other controllers can be processed in a way that meets performance and EMC requirements.

The cable length and diameter should match: 1 mm ² (18 AWG) for cables not exceeding 15 meters, 1.5 mm ² (16 AWG) for cables between 15-25 meters, and 2 mm ² (14 AWG) for cables between 25-40 meters. The wire from LECM to the valve does not require shielding, but it must be twisted pair, at least 30 twists/meter, and the insulation outer diameter must meet the LECM joint sealing requirements. No live plugging or unplugging is allowed in hazardous areas; The on-site wiring should withstand at least 105 ° C; the coil grounding terminal should be grounded.

Four step bench testing for rapid isolation issues

When suspecting a problem with Sogav 250, first remove the valve and perform four tests in sequence. If all four items pass, the problem is likely not with the valve, so do not continue to disassemble.

The first step is to measure the coil resistance. At room temperature, measured from the two pins of the connector, the MS connector and flying wire version of Sogav 250 are both 1.1-1.3 Ω, with slight differences in flying wire length. Due to the low resistance, the probe resistance must be deducted; It can also be compared with known good valves. If it exceeds the range, replace the E-core coil component. Measure the resistance from any needle to the electromagnet housing again, which should be infinitely high; Sometimes the initial reading is greater than 10 M Ω and gradually rises to infinity, indicating that the meter is charging the coil capacitor, not a fault. If low resistance occurs, it indicates a short circuit to ground, and the coil component should be replaced.

The second step is to conduct a valve leakage test. Install a pressure connector and a suitable O-ring at the air inlet, add 150 kPa/1.5 bar of air, and listen to the outlet in a quiet place. If you cannot hear or only hear reluctantly, the valve is normal; If there is a significant leakage, it may be due to damage to the valve plate or contamination between the plates, and it needs to be disassembled for inspection and treatment. The flow meter should be less than 2.83 m ³/h (100 SCFH).

Step three, measure the intensity of the action. Apply 150 kPa/1.5 bar air pressure, use a power supply that can output 16 A and 110 VDC, limit the current to 16 A, and limit the voltage to be greater than 110 VDC, with a series switch. After the switch is instantly turned on and immediately turned off, hearing a loud "bang" sound like a balloon bursting indicates sufficient power. Note that the power on of 16A should not exceed 2 seconds; Two rapid and continuous 1-second pulses are equivalent to one 2-second pulse, with a 1-minute cooling interval between the pulses. The actual In Pulse driver can only be powered on for a maximum of 0.0032 seconds at 16 A each time, which cannot be achieved by manual switching, so strict time limits must be implemented. If there is no loud "bang" sound and the current is applied correctly, it may be due to loose screws between the armature and the dynamic measuring plate, foreign objects between the dynamic plate and the upper plate, or foreign objects between the armature and the E-core, which should be disassembled for inspection and evaluation.

Step four, measure the valve stroke. Bottom load version only: First confirm that the outlet seat ring is flush with the valve housing surface. Set the power current limit to 6 A without adding air pressure. After the switch is turned on, quickly reduce the current to 2 A (2 A can be continuously powered on without overheating). Measure from the valve bottom flange to the dynamic measuring plate surface using a depth micrometer or dial gauge; After the power is cut off, the difference is the stroke, which should be 0.49-0.52 mm. The diameter of the measuring rod is less than 3 mm, and it extends into the outlet hole of the lower stop measuring plate, passes through the panel slot, and touches the plate surface. If the stroke is less than 0.48 mm, it is likely that there are foreign objects between the moving plate and the upper plate or between the armature and the E-core; If it is greater than 0.52 mm, there may be wear and tear, and it should be disassembled for inspection and evaluation.

Four items still pass abnormally, check again: whether the pressure difference between the two ends of the valve exceeds 150 kPa/1.5 bar, overpressure will prevent suction; Whether the cables and joints are in good condition, and the resistance of each wire should be less than 0.4 Ω; Whether the wire is eroded, whether the joint is loose or intermittent; Are the controller timing and driver settings correct.

Application system and pressure difference limitation

The maximum pressure difference from the gas manifold to the air manifold of Sogav 250 unbalanced valve is 150 kPa/1.5 bar, beyond which the valve may not open. At low loads, the pressure difference should be small to avoid a very short opening duration, which can lead to a decrease in mixing uniformity and an increase in valve to valve differences; At full speed and load, a high pressure difference is usually required to supply sufficient fuel within the allowed time. If the load drops significantly without reducing the gas manifold pressure, the pressure difference may exceed the limit and the valve will not work. Therefore, the main engine controller must simultaneously control the air manifold pressure and gas manifold pressure: the air pressure is controlled by the throttle/actuator or exhaust bypass to control the air-fuel ratio, while the gas pressure regulation ensures reasonable pressure difference under different operating conditions.

In terms of timing, after the overlapping period of scavenging, the Sogav quickly opens after the exhaust valve is closed, and the gas enters the intake duct and enters the cylinder with the air; Control relies on the duration of activation. The valve must be closed early enough before the intake valve is closed, otherwise the gas remaining in the intake duct will be discharged into the exhaust during the next overlap period, wasting fuel and increasing unburned hydrocarbons. Engineers need to determine the opening time and maximum allowable duration, with the valve as close as possible to the intake valve and the connecting passage as short as possible.

When estimating flow rate, the gas flow equation can be used for subcritical flow; When P2/P1 is less than 0.544, it enters the blocked flow and is calculated using 0.544 instead of the actual ratio. For example, when k=1.31, sg=0.55, P1=4.5 bar, P2=3.0 bar, and Tg=20 ° C, the steady-state fully open flow rate is about 538 g/s. This example can be used to determine whether the valve specifications and pressure difference match.

Key points for replacement and maintenance

Confirm the model before replacement: unbalanced bottom load, unbalanced top load, or balanced top load; MS connector or fly wire; Is the coil resistance consistent with the part number. Do not directly swap different structural versions. At least retest after replacement: installation of O-ring, screw torque, grounding, coil resistance, ground insulation, leakage, actuation strength, stroke; The bottom version also needs to confirm that the seat ring is flush. Before the first gas supply, use air or inert gas to check for leaks and confirm that there are no leaks before starting.

The lifespan of Sogav valves is related to speed, fuel quality and pollutants, filtration, temperature, vibration, driving electronics, fuel oil content, and installation direction. The recommended fuel oil content is at least 2 ppm; Below 2 ppm, the coated version should be selected. The maintenance/refurbishment cycle is determined by the engine manufacturer based on the application; The best way is to return to Woodward for refurbishment with specialized equipment and test benches. On site inspections are only allowed and on-site dismantling is not recommended.

In terms of safety, the gas manifold should be immediately depressurized and emptied after the engine is stopped to prevent gas from leaking into the air manifold through the valve, which may cause excessive concentration during the next start-up. Stop the machine immediately upon discovering a leak, blow the fuel system, check for leaks, and repair them; If the leakage source is Sogav, replace the faulty valve. Confirm that there are no leaks and the leak detection system is functioning properly before restarting.

Quick specification check and on-site inspection checklist

Key specifications: Operating temperature range of -20 to+105 ° C for some models, -20 to+95 ° C for some models; Storage range of -40 to+70 ° C; Humidity ≤ 85% non condensing; Protection IP66; At an altitude of 4000 meters, the response time for fully open/fully closed should not exceed 0.0050 seconds; Close the leakage to less than 0.25% of the rated steady-state flow rate; The filtration requirement is an absolute maximum particle size of 5 μ m; The maximum gas supply pressure is 450 kPa absolute pressure; Maximum air manifold pressure 300 kPa absolute pressure; Maximum pressure difference of 150 kPa; The peak of tempering pressure should not exceed 50 kPa above the current gas manifold pressure, and exceeding 2 bar may damage the valve; The maximum gas temperature is 80 ° C.

On site inspection checklist: 1) Work after power and gas outages; 2) Confirm valve model and connector; 3) Check the cleanliness of the O-ring and installation surface; 4) Tighten M10/3/8 and M8 × 1.25 with torque; 5) Reliable grounding; 6) Measure the coil with a resistance of 1.1-1.3 Ω and connect the probe; 7) Measure ground insulation; 8) 150 kPa leakage test; 9) 16A instantaneous actuation test, strictly limited time; 10) Measure the stroke of 0.49-0.52 mm; 11) Check if the pressure difference exceeds 150 kPa; 12) Check that the cable is less than 0.4 Ω and the joint is not corroded; 13) Confirm that the shielding grounding method matches the controller; 14) After shutdown, the gas manifold is depressurized and emptied.

In the order of "safety first, testing later, electrical circuit first, valve body later", Sogav 250's non opening, internal leakage, weak response, abnormal travel, and re inspection after replacement can mostly be quickly located. When passing the four bench tests, attention should be turned to differential pressure, wiring harness, connectors, and controller timing to avoid ineffective valve disassembly.