Attachment sales are where good machines get ruined. A breaker that is one size too large for the carrier will run, and it will destroy the pump over two seasons. A pulverizer plumbed into a one-way circuit will rotate the wrong way, or not at all. And a grapple fed through a hose that is one size too small will feel weak no matter what the relief is set to. This is a selection problem, not a repair problem, and it is worth an hour of arithmetic before the attachment is ordered — the arithmetic Guangzhou Shenyue Machinery Technology Co., Ltd. runs with customers before quoting any piping.
Start with the pump, not the brochure
The attachment seller quotes a required flow and a working pressure. Your machine has a pump that delivers a certain flow at a certain pressure, and an auxiliary circuit that may or may not be able to pass all of it. Three numbers have to line up: what the attachment needs, what the pump can give at that pressure, and what the auxiliary circuit and hoses can carry without choking.
On a 20-tonne Kobelco the main pump is typically the K3V112DT family, and on the 30-tonne class the K5V140. Those two families are not the same pump and do not share attachment behaviour — a detail worth checking before you copy a breaker setting from one machine to another. Our K3V112 versus K5V140 comparison explains the difference, and the hydraulic components range lists the pump assemblies we hold.
Which circuit does the attachment need?
| Attachment | Circuit | What decides the install |
|---|---|---|
| Hydraulic breaker | One-way, single-acting | Return line size and back pressure; breaker needs a free return, not a restricted one |
| Pulverizer, shear, rotating grapple | Two-way, double-acting | Both ports must be plumbed to the auxiliary spool; rotation needs its own circuit or a diverter |
| Vibratory plate compactor | Two-way, motor-driven | Case drain, and a relief that protects the motor rather than the cylinder |
| Quick coupler | One-way, low flow | Pressure hold and a check valve; a coupler that drifts open is a safety issue |
Relief setting: the number people get wrong
The main relief protects the machine. The circuit relief protects the attachment. If the attachment's own relief is set above the carrier's, the attachment becomes the weakest component in the system and something else fails first — usually a hose or a pump. Set the circuit relief to the attachment manufacturer's figure, then verify at the gauge with the attachment working. Breakers in particular are sensitive to back pressure on the return: a restricted return raises the internal pressure the breaker sees and shortens seal life dramatically.
Hose sizing, without guessing
Hose bore is chosen by flow and by the velocity you are willing to accept. Keep pressure lines at or below roughly 5 to 6 metres per second and return lines lower than that. A hose that is one size too small turns the excess into heat and pressure drop, and the machine reads as underpowered.
| Flow through the line | Bore usually adequate | Watch for |
|---|---|---|
| Up to about 60 L/min | 1/2 inch | Long runs and elbows push velocity up |
| About 60 to 120 L/min | 3/4 inch | Return lines often need the next size up |
| About 120 to 200 L/min | 1 inch | Fitting bore is often smaller than hose bore — check both |
These are rules of thumb for selection conversations, not a substitute for the hose maker's pressure and velocity tables; confirm the rating with the supplier before a line goes into service. The hose part number guide published earlier this week on this blog explains why the exact suffix on the number matters when you replace one.
Heat, and the part nobody budgets for
An attachment working continuously adds heat the machine was not designed to reject at that duty. If the breaker runs all day in summer, oil temperature becomes the limiting factor, and the first symptoms are tired travel and a slow boom at the end of the shift. Read the overheating diagnosis notes before blaming the attachment. For machines on this kind of duty, plan the cooler and the oil change interval together with the attachment.
For circuit protection detail — accumulators, crossover reliefs and the safety side of breaker and shear installation — see our breaker and shear circuit guide. Machine flow and pressure ratings for your serial belong to Kobelco, and if you are specifying a machine for a bauma China visit, the official show site lists the exhibitor programme.
Guangzhou Shenyue Machinery Technology Co., Ltd. supplies the piping, hose, relief and pump parts around an attachment installation, and says plainly on every quotation whether an item is genuine, OEM or aftermarket. We are an independent supplier and are not affiliated with Kobelco Construction Machinery Co., Ltd.
Frequently Asked Questions
Can I run a breaker on a Kobelco without a dedicated auxiliary circuit?
Only if the machine has an auxiliary spool and piping rated for the breaker's flow. Teeing into a boom cylinder circuit is not a substitute: the breaker needs a free return, and a restricted return raises internal pressure and shortens seal life. Check the auxiliary circuit and the relief figure before the breaker is ordered.
What size hose do I need for a 120 L/min attachment circuit?
As a rule of thumb, 3/4 inch bore is the starting point at that flow, with return lines often one size larger. Fitting bore can be smaller than hose bore, so check both, and confirm the pressure rating with the hose supplier before the line goes into service.
Should the circuit relief be set higher than the machine relief?
No. The circuit relief protects the attachment and should follow the attachment manufacturer's figure, which is normally below the carrier's main relief. If the attachment relief is set higher, the hose or the pump becomes the weakest part of the system.
Do pulverizers and grapples need a case drain?
Motor-driven attachments such as pulverizers, rotating grapples and compactors generally do. Without a case drain the motor seal is pressurized and fails early. Guangzhou Shenyue Machinery Technology Co., Ltd. asks for the attachment model and the existing piping photographs before quoting the hoses and fittings.