Are there any simple tests you can carry out to check servo valves?

If the cylinder moves then there is every chance that the servo valve is OK. This simple test only shows the valve is basically functional, it will not show some of the more subtle faults the valve can have. If you get no movement then the valve is probably faulty, at this point check pressure is present at the “P” port. If you have more than 5 machines buy a servo valve tester (try Simply plug it in and the valve and cylinder should move.

Some servo valves can be accidentally fitted 180 degrees out of position (Moog 62, 76 and 760 series for example). If the hoses have been off for any reason check they are the correct way round. If the pressure is on the correct port of the servo valve and the cylinder rod is not seized (very unlikely) then the servo valve is probably faulty.

How often should servo valves be serviced?

Servo valves are highly dirt sensitive and often many companies have inadequate maintenance standards. Always change filter elements when the dirt alarm switches or the pop up shows. Armageddon. Cleanliness is next to godliness when it comes to hydraulic fluid and servo valves, i.e. it should meet ISO 16/13/9 standards for most applications. Dirty hydraulic fluid is the often at the base of servo valve troubles and therefore servo valves can be used for long periods without being service if you ensure that the fluids used are in good conditions.

Blow Moulding Soup of the Day 1

Some hints and tips relating to Moog parison programmers AND occasionally ‘weird stuff’ that won’t necessarily relate directly to the products or services we sell.

Of servo valves

  1. Many blow moulding machines use the Moog 76 & 760 series servo valve for parison control. Experience has shown that Moog’s 62 and 631 series valves are less dirt sensitive, less expensive to buy and service. Ask us about our exchange program.
  2. Never ever try and take the spool out of a servo valve – you will probably wreck to valve.
  3. Most Moog servo valves we get in for repair are damaged by heat, not blocked with dirt. Is your oil cooler blocked ? Do they forget to turn the cooling water on after a mould change?
  4. NUMBER CRUNCHING: Moog servo valves cost thousands of dollars, but 10% of the valves sent to us have no details of who sent it!
  5. Servo valve problems? Check that the filter dirt alarm switches are connected – they often aren’t Better still don’t fix the cause of the problem, just keep sending the servo valves to us for repair – we need the money.
  6. When sending valves to us for repair ask your engineers to fit a cover plate. Without the plate residual oil can make the box soggy and the valve falls out. The shippers insurance does not cover this as it was your fault. If fact he can charge you for the damage caused to other shipments. Insufficient packing is your fault.
  7. Trouble with Moog valves? You might be using one of the older types that are more dirt sensitive than newer models. Tell us what you’ve got, we’ll tell you if it’s the best servo valve for the job.
  8. LVDT transducers don’t go faulty as often as you might think! Unless the wires get damaged or you bash it then the transducer might be OK. Testing is easy.
  9. Companies that have fitted ‘off line’ continuous hydraulic filter units are all reporting a significant reduction in hydraulic problems. Don’t buy a mobile filter trolley for filtration. The only use of these units is filling up the hydraulic tank.
  10. Moog valve arrived today, hanging out of the box. Damage over $600. Not covered by DHL insurance as the valve had no cover plate and the oil leaked out, box got soggy. DHL considering charging for damage to other parcels.
  11. When sending Moog or other servo valves to us for repair, fit the cover plate (We know you have some !)