How the Hydraulic System Is Put Together

Most crane pages talk about reach. This one is about the circuit, because on a compact machine the circuit is what you actually feel in the seat.

The architecture on our Hydraulic Small Spider Crane is deliberately conventional. Not because we cannot design something cleverer, but because a circuit an on-site fitter understands is worth more than a clever one they cannot repair.

Power source. A gear pump driven off the engine or electric motor delivers a constant 20 L/min. Gear pumps are simple, cheap to replace and tolerant of ordinary dirt. On a small machine that beats a load-sensing piston pump on serviceability every time.

Pressure control. A main relief valve caps system pressure at 21 MPa. Everything downstream is rated above that, so the relief is the weakest link by design — that is the point.

Distribution. A proportional directional valve feeds the boom telescope, boom lift, slew motor and winch. Proportional spools let flow ramp smoothly instead of snapping open, which is where smooth motion comes from.

Load holding. Boom lift and outrigger cylinders sit behind counterbalance or pilot-operated check valves. If a hose lets go, the cylinder does not run away. This is a safety layer that works even when the operator does nothing.

Return path. Oil passes a 10 micron return filter and an air-cooled cooler before it goes back to a baffled 40 L reservoir.

That chain — pump, relief, proportional valve, counterbalance, filter, cooler, tank — is the whole machine as the operator experiences it. Everything else is steel.

Key Components and What They Do

If you remember one thing from this page: the return filter is cheaper than the valve block by two orders of magnitude, and it is the component standing between ordinary grit and a four-figure repair. Change it on schedule.

Micro-Control: Why Slow Is a Feature

Buyers sometimes ask why we quote a minimum controlled speed of 0.05 m/min instead of just "fast winch". The answer is that "fast" is easy and useless on the jobs a small spider crane actually does.

Three mechanisms make slow control workable.

Meter-out control on the lowering side. The valve restricts oil leaving the cylinder rather than entering it. The load stays supported by hydraulic pressure at all times, so the boom cannot run away downhill.

Constant-pressure supply. Because the gear pump runs at fixed flow and the proportional spool bleeds only what is needed, supply pressure stays steady even as you feather the lever. No lurch when you crack the valve.

Counterbalance valves sized to the actual cylinder load. A valve set too soft makes a boom feel spongy. Ours are matched, so the boom holds a position firmly with the lever centred.

On the ground this shows up in tasks that are otherwise miserable. Setting a curtain wall frame into a bracket. Dropping a pump skid onto four anchor bolts. Landing a glass unit on a vacuum lifter without a bounce. Placing a machine tool so the base contacts the plinth evenly rather than on one corner first.

We tested this routinely during development by landing a loaded pallet onto a coin standing on end. It is a slightly silly test. It is also the fastest way to show a customer which machines they can trust near finished surfaces, and ours pass it.

Specifications

Hydraulic Maintenance and Oil Management

Oil is the component nobody photographs and everybody depends on. On a Hydraulic Small Spider Crane, four habits keep the circuit healthy for a decade.

Sample at 500 hours. A laboratory oil report tells you water content, particle count and additive depletion before you can feel any of it in the lever. Cheap early warning.

Change oil at 1,000 hours or annually, whichever comes first. In dusty environments, drop to 750 hours. Use ISO VG 46 unless ambient conditions say otherwise, and never mix grades to top up.

Keep the 40-60 C band. Below that, oil thickens and the pump strains on start-up in winter. Above it, viscosity drops and internal leakage grows. The cooling system on our machine is sized to hold that band in typical summer working conditions; if you work in 40 C ambient, tell us at order stage.

Protect the fill point. Ninety percent of contamination enters through the filler cap or during a sloppy top-up. Wipe around the cap, use a filtered fill pump, and never leave the reservoir open in a dusty workshop.

Two more items worth putting on your own board. Replace the breather when the desiccant turns colour, since a saturated breather pulls moisture into the tank. And torque-check hydraulic fittings after the first 50 hours of a new machine, because that is when thermal cycling settles them.

Troubleshooting: Reading the Symptoms

The pattern in this table is worth noticing. Almost every hydraulic fault announces itself as a change in behaviour weeks before it becomes a breakdown. A winch that sounds slightly different on Tuesday is telling you something. Operators who mention it get a filter change; operators who wait get a valve rebuild.

FAQ

Q: What hydraulic oil and pressure does this machine use?

A: System pressure is 21 MPa and the standard oil is ISO VG 46, with VG 32 for cold climates and VG 68 for sustained high ambient temperatures. Reservoir capacity is 45 litres and return filtration is 10 micron. We list the recommended brand-neutral specification in the manual so you can source oil locally.

Q: I have found oil under the machine. How do I trace it?

A: Wipe everything dry, run the machine through each function for a short cycle, then look for fresh traces at fittings, cylinder glands and the valve block. The most common sources are a loosened fitting after thermal cycling, a weeping cylinder rod seal, or a pinched O-ring at the valve stack. Send us photos and the serial number and our technical team will narrow it down before you take anything apart.

Q: Can I start the machine below freezing?

A: Yes, with two precautions. Use ISO VG 32 oil for cold-season operation, and allow a warm-up cycle at low idle with no load until the oil reaches about 30 C. For regular work below -10 C, order the pre-heat kit, which brings the reservoir up to temperature before you begin lifting and avoids pump cavitation on a cold start. Machines built by JOJOmechanical for Nordic and Canadian customers ship with this option as standard.