Troubleshooting Sequence Valves Sequence valves have an important role to play in hydraulic systems. They control flue flow to both the primary and the secondary circuits. They also control the sequence that particular events occur and maintain the pressure of the primary line. It’s important to remember that the pressure of the sequence valve should never be below 200 psi of the system relief valve setting. When it comes to sequence valve troubleshooting, you’ll need to add pressure gauges to both the primary and secondary ports of the valve. Most valves have a gauge port installed in the unit. You’ll use the readings of the pressure gauge to understand what is occurring in the sequence valve. If there are contaminants in the hydraulic fluid it can have a negative effect on the sequence valve. It can block internal pilot fluid passage and moving parts can wear down faster. There are a number of ways that the sequence valve can malfunction: You may experience premature valve shifting. This can occur when the fluid is not flowing at a high enough pressure. You’ll need to check the sequence valve to confirm if there is a blockage of the drain hole in the main spool. This would allow pressure to build in the spool cavity and therefore shift the spool at the incorrect time. Also check whether the spool is stuck open because it has been damaged or it has contaminants stuck on it. If you are getting too much pressure in your valve, it’s time to check the sequence valve itself. Check whether the pilot control piston is getting stuck. This could be down to contaminants or even scoring. It could also be that the fluid passage of the pilot has collected contaminants and therefore the pressure is too low to shift the spool. Any fluctuations in pressure could be down to contaminants or the improper sized drain line. If you have any experience in the area of sequence valve troubleshooting, feel free to comment below.