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March 24, 2026

Hydraulic Lockout: LOTO for Hydraulic and Pneumatic Systems

Accumulators, trapped oil and raised loads keep pressure after shutdown. The hydraulic lockout order that releases them, the EU and Swiss rules, and the devices for each valve.

Hydraulic Lockout: LOTO for Hydraulic and Pneumatic Systems

A hydraulic lockout is not complete when the pump stops: oil stays under pressure in lines, cylinders and accumulators, and a load held up by a cylinder keeps it there. General machine building runs hydraulics at up to 350 bar, and some forming presses at up to 5,000 bar.[1]

Table of Contents
  1. Why Pressure Stays After the Pump Stops
  2. Hydraulic Lockout, Step by Step
  3. Accumulators, Trapped Oil and Raised Loads
  4. Machines With Hydraulics and Pneumatics
  5. What EU, German and Swiss Rules Require
  6. Where The Lock Box Fits

Before the first padlock goes on, the machine's procedure has to answer three questions:

  1. Which pumps, power units and air supplies feed the machine, and where is each isolation point?
  2. Are there accumulators, or cylinders that hold a load once the power is off?
  3. Where are the gauges, and which valves need a lockout device because they cannot take a padlock?

Part 1: Why Pressure Stays After the Pump Stops

Unlike an electrical isolator, a closed hydraulic valve only stops new energy coming in: what is already in the circuit stays. DGUV, the German statutory accident insurance, lists where it remains: hydraulic or pneumatic accumulators, raised loads, clamping forces and parts braced against each other.[1]

Oil escaping from a crack under high pressure causes very serious injuries or poisoning, and protective clothing, gloves included, does not fully protect.[1]

Where energy remains Why it stays How to make it safe
Supply lines Another circuit can feed them Close and lock the isolation valves
Accumulator Holds oil under gas pressure Discharge or isolate it; read the gauge
Oil between valves Nothing vents it Operate the valves several times
Cylinder holding a load Gravity keeps the oil under pressure Lower the load or support it
Compressed air Air stays in lines and receivers Lock the air valve closed, exhaust the circuit

Part 2: Hydraulic Lockout, Step by Step

DGUV's "five-finger rule of fluid power" sets the order.[1] For the general sequence, see the 6 (and more) steps of lockout tagout.

  1. Interrupt the energy supply. Tell the operators, stop the machine with its normal controls, then switch off the pump motor at its isolator.
  2. Prevent reconnection. Lock the isolator off with your personal padlock. Close each hydraulic isolation valve and lock it with a hydraulic valve lockout; DGUV's own example shows lockable ball valves.[1]
  3. Depressurise. Release the system pressure, every accumulator included, lower or support raised loads, and release trapped oil (Part 3).
  4. Check. The gauges read zero, the controls produce no movement and loads rest on their supports. Return the controls to off.
  5. Prevent hazards from adjacent systems. Make sure a neighbouring machine or shared power unit cannot feed your circuit.

Treat the check as work on a pressurised system.[2] Loosen fittings slowly; if oil comes out under pressure, stop, relieve it again and recheck.[1] This is the tryout in LOTOTO (lockout, tagout, tryout).

Best Practice: Lock the bleed valve open as well as the isolation valve closed. INRS, the French safety institute, lists both.[2] If the isolation valve leaks, the open bleed keeps the isolated section at atmospheric pressure.

Part 3: Accumulators, Trapped Oil and Raised Loads

Accumulators

Release the accumulator pressure with the system pressure, automatically or with the manual relief valve on the safety block, and confirm it on a gauge. The gas side can still be under high pressure: before an accumulator is removed, relieve both the oil and the gas side. Only trained technicians or the manufacturer should work on accumulators.[1]

Trapped oil

Pressure can remain in oil trapped between valves. Release it by operating the valves several times, or as the manufacturer specifies. On a cylinder, relieve both the piston side and the rod side.[1]

Raised loads

A press ram, lift table or vertical axis held by a cylinder keeps the circuit under pressure. Lower the load, secure it with the machine's own locking device, or support it safely.[1] Where a support or locking pin takes a padlock, lock it in place.[2]

Real-World Case: The German IFA investigated a fatal accident on a hydraulic lift table. Fitters had hoisted the table up and propped it to change the pump motor. When one removed the props, the table fell at high speed and killed him: hoisting had drawn a partial vacuum in the cylinders, so the safety valves could not hold the load. IFA's advice: unless you are sure the system is full of oil, hold the table from above and below for the whole job.[3]

Part 4: Machines With Hydraulics and Pneumatics

A hydraulic press with pneumatic clamps needs both energies in the procedure, each with its own isolation point and check. Lock out the pump and compressor motors first: a fluid isolation only holds once the energy driving the flow is off.[2]

On the air side, lock the supply valve closed, exhaust the circuit and read the gauge. Where air arrives through a coupling, an air source lockout such as our Stainless Steel Air Source Lockout stops it being reconnected. Receivers and bleed-down are covered in our guide to pneumatic lockout.

Part 5: What EU, German and Swiss Rules Require

  • Machinery Directive 2006/42/EC, Annex I, 1.6.3: machines need means to isolate them from all energy sources, lockable where reconnection could endanger people, and stored energy must be capable of being dissipated without risk.[4] Regulation (EU) 2023/1230 replaces the Directive from 20 January 2027.[5]
  • EN ISO 14118, clause 3.3: isolation and energy dissipation means isolate, lock, dissipate or restrain stored energy, and verify.[6]
  • EN ISO 4413 and EN ISO 4414: the design standards for hydraulic and pneumatic systems, with requirements for gas-loaded accumulators and their warning label (4413, 5.4.3 and 7.3.2.1)[7] and for positive isolation from energy sources (4414, 5.2.8).[8] Missing lock points or gauges are a question for the machine builder.
  • Germany and Switzerland: DGUV Information 209-070 gives the five-finger rule in Part 2.[1] Suva's vital rules for maintenance: switch off all energy sources and lock with your personal padlock (rule 3); make stored energy, such as an unsecured raised load, harmless (rule 4).[9]
  • US, for comparison: OSHA 29 CFR 1910.147(d)(5)(i) requires stored energy to be relieved, restrained or otherwise made safe.[10]

Part 6: Where The Lock Box Fits

Besides the motor isolator, hydraulic isolation points are valves, so hydraulic lockout equipment starts with valve lockouts:

Write every isolation point, how stored pressure is released and how zero pressure is checked into the machine's own procedure with our free lockout/tagout procedure template (PDF, Word or Excel).

Need Devices for a Hydraulic Machine?

Contact The Lock Box with the valve types and sizes at your isolation points, and we will propose the devices.

References

  1. DGUV. DGUV Information 209-071: Safe maintenance of hydraulic systems (English edition of DGUV Information 209-070), June 2019, pp. 9, 16, 19-20, 29, 55, 61 and 66-68. https://publikationen.dguv.de/widgets/pdf/download/article/255
  2. INRS. ED 6109: Consignations et déconsignations, 3rd edition, October 2020, sections 4.1, 6.1 and 7.1. https://www.inrs.fr/dam/inrs/CataloguePapier/ED/TI-ED-6109.pdf
  3. IFA (DGUV). Safety risks of maintenance work on hydraulic machinery, Aus der Arbeit des IFA no. 0185, edition 1/2015. https://www.dguv.de/medien/ifa/en/pub/ada/pdf_en/aifa0185e.pdf
  4. European Union. Directive 2006/42/EC on machinery, Annex I, section 1.6.3: Isolation of energy sources. https://eur-lex.europa.eu/eli/dir/2006/42/oj
  5. European Union. Regulation (EU) 2023/1230 on machinery (applies from 20 January 2027). https://eur-lex.europa.eu/eli/reg/2023/1230/oj
  6. ISO. ISO 14118:2017 (EN ISO 14118:2018): Safety of machinery, Prevention of unexpected start-up, clause 3.3. https://www.iso.org/standard/66460.html
  7. ISO 4413:2010 (EN ISO 4413:2010): Hydraulic fluid power, General rules and safety requirements for systems and their components, clauses 5.4.3 and 7.3.2.1 (table of contents at DIN Media). https://www.dinmedia.de/en/standard/iso-4413/136949252
  8. ISO 4414:2010 (EN ISO 4414:2010): Pneumatic fluid power, General rules and safety requirements for systems and their components, clause 5.2.8 (table of contents at DIN Media). https://www.dinmedia.de/en/standard/iso-4414/136949268
  9. Suva. Acht lebenswichtige Regeln für die Instandhaltung (Eight vital rules for maintenance), 84040.d, revised March 2022, rules 3 and 4. https://www.suva.ch/84040.d
  10. OSHA. 29 CFR 1910.147: The control of hazardous energy (lockout/tagout), paragraph (d)(5)(i). https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.147
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