Shaking hoses, gas loss, stuck chisel or overheating

Violently shaking hoses mean low nitrogen or a damaged diaphragm. Gas that will not hold points to a damaged charging-valve O-ring, back head O-ring or gas seal. A chisel sticks or breaks from missing grease, angled blows, prying, a worn bush or blank firing. Overheating comes from engine speed too high, flow above the rated range or a dirty cooler.

Field Guide

Hammer troubleshooting

Q: The hammer hits weakly or slowly

Common causes are low nitrogen, low carrier pressure, oil above 90 °C, a frequency valve set too tight, not enough down-force, or a worn chisel or bush. Raise nitrogen in 2 kg/cm² steps, have the relief and pump pressure set by a technician, keep oil at 60–80 °C, and replace the bush once the gap exceeds 6 mm on small models or 8 mm on large ones.

Your hydraulic hammer stopped working, or it hits weakly? Run these checks first. Most hammers that “won’t work” only need commissioning, not repair.

Start the checks Download the PDF

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hydraulic hammer troubleshooting

Step 1

The 60-second checks

Six things to confirm before anything else. Tick them off as you go; you will need the answers if you contact us.

Hoses and valvesPressure line on IN, return on OUT, and both shut-off valves on the arm fully open.
Oil level and conditionTank full, oil clean, not milky or dark.
Oil temperature60–80 °C after 10 minutes of work. Never above 90 °C.
Nitrogen chargeBack head reads 16–17 kg/cm² (230–240 psi) when cold.
GreaseChisel pressed up into the front head and greased. Do this every 2 hours of work.
Chisel and pinsChisel slides freely, pins not bent, no cracks or mushrooming.

0 of 6 checked.

Step 2

Find your symptom

Open the one that matches, and work through it in order. Stop as soon as the hammer runs properly.

AThe hammer will not strike

Almost always a commissioning problem on a new install: pressure, flow or nitrogen.

1 · Check pressure and flow

Measure the pressure in the hammer line, or read the carrier’s gauge, and compare with the table below. Too little pressure or flow is the most common cause.

2 · Re-commission the nitrogen

Release the back head nitrogen down to 3–10 kg/cm² (43–142 psi), or empty it.
Press the chisel down onto the material and test-fire.
Once it strikes, recharge in steps of 2 kg/cm² up to 16 kg/cm² (230 psi), testing as you go.

3 · Reverse the lines briefly

Empty the nitrogen.
Swap the IN and OUT hoses and fire for no more than 1 minute to free a stuck valve.
Reconnect the hoses the correct way round, test, then recharge the nitrogen.

CautionNever leave the hoses reversed, and keep everyone away from the front of the chisel during these tests.

4 · Still nothing

Dirt has probably reached the control (reversing) valve. It needs flushing or replacing by a hydraulic technician. Contact us with the details at the bottom of this page.

BThe hammer hits weakly or slowly

Cause	How to check	Fix
Low nitrogen	Read the back head charge cold.	Raise it in 2 kg/cm² steps to the value in the table below.
Low carrier pressure	Measure at the hammer line.	Have the relief and pump pressure set by a technician.
Oil too hot	Read the temperature after 10 minutes.	Keep 60–80 °C. Above 90 °C stop and cool. Replace tired oil; VG 46 cold, VG 68 hot.
Frequency valve too tight	Models from the JMASB81EBH up have an FM adjuster.	Quarter turn at a time: clockwise slows the blow rate, counterclockwise speeds it up.
Not enough down-force	Watch the carrier’s front while breaking.	Press down until the front just lightens; keep the chisel at 90°.
Worn chisel or bush	Check the gap between chisel and front bush.	Replace the bush over 6 mm (small models) or 8 mm (large).

Good to knowA mismatch between hammer and carrier pressure is normal on a new install. It is corrected by commissioning, not by repair.

COil leaks after the hammer has stood

The main oil seal was crushed by the way the hammer was stored, or it has simply aged. Expect to change the main seal every 800–1,000 hours or 3–6 months, depending on how hard the hammer works.

How to store a hammer

Release all nitrogen from the back head, and from the accumulator on large models.
Remove the chisel.
Push the piston fully in with a round bar, then grease the front head well.
Lay it flat on timber, cap the hoses, keep it under cover.

DOther faults: shaking hoses, gas loss, stuck chisel, overheating

Symptom	Likely cause	Fix
Hoses shake violently	Low nitrogen in the back head or accumulator; damaged diaphragm.	Stop work, check and recharge. Replace the diaphragm if it will not hold.
Irregular blows	Too little down-force, hot oil, high back pressure, worn chisel or bush.	Fix the technique first, then check cooler, filter and bush wear.
Gas will not hold	Damaged charging-valve O-ring, back head O-ring or gas seal.	Replace the O-rings from the seal kit; test with soapy water.
Chisel sticks or breaks	No grease, angled blows, prying, worn bush, blank firing.	Grease every 2 hours, keep the chisel square, never pry, replace the bush.
Hammer overheats	Engine speed too high, flow above range, dirty cooler.	Run at rated rpm, set the flow, clean the cooler.

Before any disassemblyEmpty the nitrogen from the back head, and from the accumulator before touching its screws, then remove side bolts and through bolts. Stored gas can cause serious injury.

Reference

Flow, pressure and nitrogen

What the carrier must deliver at the hammer, and what the gas charge should read cold. These are the same figures shown on each product page; the last column is the ceiling the hammer must never run above.

Model	Chisel Ø	Flow (L/min)	Flow (GPM)	Operating pressure (kg/cm²)	Operating pressure (psi)	Never exceed
JMASB20EBH	45 mm	20–30	5.3–7.9	90–120	1,280–1,707	140
JMASB30EBH	53 mm	25–50	6.6–13.2	90–120	1,280–1,707	140
JMASB40EBH	68 mm	40–70	10.6–18.5	110–140	1,565–1,991	160
JMASB43EBH	75 mm	50–90	13.2–23.8	120–150	1,707–2,133	160
JMASB50EBH	100 mm	80–110	21.1–29.1	150–170	2,133–2,418	200
JMASB60EBH	125 mm	90–120	23.8–31.7	150–170	2,133–2,418	220
JMASB81EBH	140 mm	120–180	31.7–47.6	160–180	2,276–2,560	240
JMASB121EBH	155 mm	180–240	47.6–63.4	160–180	2,276–2,560	260
JMASB131EBH	165 mm	200–260	52.8–68.7	160–180	2,276–2,560	260
JMASB200EBH	200 mm	280–350	74.0–92.5	240–260	3,414–3,698	280

Back head nitrogen

JMASB20–SB50: 16–17 kg/cm², max 18
JMASB60–SB81: 17–18, max 19
JMASB121–SB200: 17–19, max 23
Standard for all models: 16.5 kg/cm² (235 psi). Adjust in 2 kg/cm² steps.

Accumulator nitrogen

Fitted on the JMASB121EBH, SB131EBH and SB200EBH. Standard 60 kg/cm² (855 psi), adjustable 55–65 as needed. It cushions the oil pressure and protects the carrier’s pump.

Operator’s manual (PDF) · Troubleshooting guide (PDF)

Support

Still not fixed?

Send us these six things and we can usually tell you what is wrong without the hammer leaving the job.

Model and serial number from the data plate
Carrier make, model and operating weight
Hours on the hammer
Measured flow, pressure and oil temperature
Nitrogen reading, back head and accumulator
A short video of the hammer running

Talk to JMA

Warranty claims: email us with the subject “WARRANTY CLAIM – [Order number] – [Model]”. We acknowledge within 2 business days and decide within 5.

Email warranty support Download this guide (PDF) Contact support