Trelawny Pneumatic Angle Grinders 4", 5" and 7"
Low Vibration 5" - 170.4054
Trelawny builds three air-driven angle grinders: a 4" at 12,000 rpm, a low-vibration 5" at 10,000 rpm, and a low-vibration 7" at 7,500 rpm. All three run at 6.2 bar and draw 8–10 cfm. The specification that decides which one you want is not the disc size - it is declared vibration, which runs from 5.1 m/s² on the 4" down to 1.2 m/s² on the 5". That single number sets how many hours a day one operator can legally stay on the trigger.
The Low Vibration 5", part by part
The 170.4054 figures on this page, pinned to the tool. Hover or tap a number to trace it to the hardware.
- 01SpindleM14Spindle lock for fast disc changes. Discs are model-specific: 491.4055 for the 5".
- 02Disc5"The larger disc covers ground faster than the 4".
- 03Air motor10,000 rpm1.7 kg and 230 mm long. 83 dB(A).
- 04Air inlet10 cfm4.72 l/s at 6.2 bar (90 psi), continuously while the trigger is held. Rear exhaust.
- 05Safety trigger1.2 m/s²Declared vibration. A full shift of trigger time stays under half the action value.
Angle Grinders
Pick the model, then add discs and brushes. Every item carries its genuine Trelawny part number (with IMPA where available) and adds straight to your quote. ShipServ TN 317548.
Which one to buy
Start from the job, not the disc size. Each card says what the tool is for, when to pick it and when to take a different one.
4" angle grinder - 170.4050
Short jobs, tight spots and the lowest purchase price.
- 1 h 55 mina day on the trigger before the action value
- 1.76 kg220 mm long
- 12,000 rpmM10 spindle
Pick it if grinding is genuinely occasional - twenty minutes here and there, a few times a week.
Take the 5" instead if one operator grinds for more than about two hours a day.
4" with wire brush head - 170.4150
The same 4" tool, supplied with a wire brush in place of the disc.
- 1 h 55 mina day on the trigger before the action value
- 1.76 kg220 mm long
- 12,000 rpmM10 spindle
Pick it if the work is de-rusting and descaling rather than disc grinding.
Take the 170.4050 instead if you need to grind with a disc. Trigger-time limits are the same.
Low Vibration 5" - 170.4054
Full shifts on one operator, and the larger disc covers ground faster.
- 1.2 m/s²a full shift stays under half the action value
- 1.7 kg230 mm long
- 10,000 rpmM14 spindle, spindle lock
Pick it if anyone is on the tool for more than a couple of hours a day. For most yard and marine maintenance work, this is the one.
Take the 4" instead if use is occasional and price matters most - the 5" costs roughly 40% more.
Low Vibration 7" - 170.4071
The biggest disc, for wide surfaces and heavier stock removal.
- 8 h or moreon the trigger before the action value
- 3.1 kgtwo-handed, 318 mm long
- 7,500 rpmslower, suits heavy removal
Pick it if you work large flat areas where the extra disc diameter pays.
Take the 5" instead if the work is overhead or in tight spaces - the 7" is appreciably heavier to hold up.
How long you can actually run each tool
Under Directive 2002/44/EC, hand-arm vibration has a daily exposure action value of 2.5 m/s² A(8) and a daily exposure limit value of 5 m/s² A(8). Reaching the action value obliges an employer to start reducing exposure and to put the operator under health surveillance. The limit value must not be exceeded at all. Member states may set stricter figures, so check your own national implementation.
Exposure depends on magnitude and trigger time together. Using the HSE points method - points per hour equals twice the square of the declared magnitude, with the action value at 100 points and the limit value at 400 - the Trelawny range works out as follows.
| Model | Declared vibration | Points per hour | Trigger time to the action value | Trigger time to the limit value |
|---|---|---|---|---|
| 4" 170.4050 | 5.1 m/s² | 52 | 1 h 55 min | 7 h 41 min |
| 4" with wire brush 170.4150 | 5.1 m/s² | 52 | 1 h 55 min | 7 h 41 min |
| Low Vibration 5" 170.4054 | 1.2 m/s² | 2.9 | 34 h 45 min | not reachable |
| Low Vibration 7" 170.4071 | below 2.5 m/s² | under 12.5 | 8 h or more | not reachable |
Read the two ends of that table against each other. Eight hours of continuous trigger time on the 4" gives a daily exposure of 5.1 m/s² A(8), which is over the legal ceiling. The same eight hours on the 5" gives 1.2 m/s², under half the action value. The 5" costs roughly 40% more than the 4". If one operator grinds for more than about two hours a day, that is not a premium - it is the difference between a job you can staff with one person and a job you cannot.
If the work is genuinely occasional - twenty minutes here and there, a few times a week - the 4" is the sensible buy and the cheaper tool is the right answer.
The caveat that goes with those numbers
A declared vibration figure is a laboratory emission value measured to a test standard. It is not a prediction of what your operator's hands will see. The HSE is explicit that declared figures are commonly lower than real in-use vibration on a worn tool, a hard material, or with an unbalanced disc. Directive 2002/44/EC does allow an exposure assessment built from manufacturer emission data combined with observation of how the work is actually done, so these figures are a legitimate starting point - but if you are close to the action value on paper, measure rather than assume.
Why an air grinder, and the air supply it needs
A 115 mm electric angle grinder costs roughly a third of the Trelawny 4". Anyone choosing the air tool is buying four specific things - and has to feed it properly.
Duty cycle
A vane motor has no thermal cut-out and no duty-cycle rating. It can be loaded to a stall and kept there without burning out, and it can run a full shift. A universal-motor electric grinder cannot, which is why yards doing continuous descaling replace them constantly.
No trailing mains cable
On a wet steel deck, in a tank, over the side of a hull, a compressed air line is easier to live with than 110 V on a cable reel - and the tools tolerate water ingress and washdown that would end an electric grinder.
Weight and balance in the hand
The 4" is 1.76 kg and 220 mm long. That matters for overhead work and in the confined spaces where most marine grinding happens.
Vibration compliance at the top of the range
The 1.2 m/s² figure on the 5" is difficult to match in a mains-powered tool at any price.
What the air supply has to deliver
Each of these tools needs its rated flow continuously, not in bursts. A 10 cfm tool running for an hour consumes 10 cfm for that hour.
- Pressure: 6.2 bar (90 psi) at the tool, not at the compressor outlet
- Flow, single tool: 4.72 l/s (10 cfm) for the 4" and 5"; 3.78 l/s (8 cfm) for the 7"
- Compressor sizing: as a trade rule of thumb, allow around 1.5× the tool's rated consumption in free air delivery - roughly 15 cfm for one 4" or 5" grinder - because rated output falls away with tank cycling, hose friction and fittings. This is guidance, not a Trelawny specification.
- Hose: use a generous bore and keep runs short. Long small-bore hose is the usual reason a tool that should be fine feels gutless.
- Conditioning: a filter, regulator and lubricator at the point of use. Water in the line corrodes vane motors; a lack of oil kills them.
Two grinders, one line
Running two grinders off one line means budgeting for both at once. This is the most common reason a new air tool disappoints on site, and it is a compressor problem rather than a tool problem.
On dust
Dry grinding of concrete, and of many coatings, produces respirable crystalline silica or hazardous coating dust. These tools have no integrated extraction, so dust control has to come from the method - wet working, a separate on-tool shroud and vacuum where one is available, or local exhaust ventilation - plus the right respiratory protection.
And the thing an air motor does not buy you
It is worth saying plainly, because it is a common assumption: replacing an electric motor with an air motor removes an electrical ignition source, but grinding throws a continuous stream of hot sparks. A pneumatic angle grinder is therefore not a solution for work in a potentially explosive atmosphere, and it does not remove the need for a hot-work permit, gas testing or a fire watch. Choose these tools for duty cycle, vibration and working environment - not as a substitute for controlling ignition risk.
Pneumatic angle grinders: common questions
How long can you use a pneumatic angle grinder before hitting the vibration action value?
With the Trelawny 4" (170.4050) at a declared 5.1 m/s², an operator reaches the daily exposure action value of 2.5 m/s² A(8) after about 1 hour 55 minutes of trigger time, and the 5 m/s² limit value after about 7 hours 41 minutes. With the Low Vibration 5" (170.4054) at 1.2 m/s², a full eight-hour shift of trigger time produces a daily exposure of 1.2 m/s² A(8) - under half the action value. Declared figures are laboratory emission values and real in-use vibration is often higher, so treat these as planning numbers.
What size compressor do you need for a Trelawny angle grinder?
The 4" and 5" models consume 4.72 l/s (10 cfm) at 6.2 bar and the 7" consumes 3.78 l/s (8 cfm), continuously while the trigger is held. Allowing the usual 1.5× margin for real-world losses, that means around 15 cfm of free air delivery for a single 4" or 5" grinder. Two grinders on one line need both allowances at once.
Is a pneumatic angle grinder safe to use in an explosive atmosphere?
No. An air motor removes the electrical ignition source, but grinding produces a continuous stream of hot sparks, which is an ignition source in its own right. Pneumatic grinders do not remove the need for a hot-work permit, gas testing or a fire watch. Choose them for duty cycle, vibration and wet or confined working conditions rather than for ignition control.
What is the difference between the Trelawny 4" and the Vibro-Lo 5" angle grinder?
Declared vibration, mainly. The 4" (170.4050) runs at 12,000 rpm with a declared 5.1 m/s² and an M10 spindle. The Low Vibration 5" (170.4054) runs at 10,000 rpm with a declared 1.2 m/s² and an M14 spindle, weighs slightly less at 1.7 kg, and adds a spindle lock and rear exhaust. Both draw 10 cfm at 6.2 bar. The 5" costs more and is the right choice wherever one operator spends more than about two hours a day on the trigger.
Why choose a pneumatic angle grinder over an electric one?
Duty cycle is the main reason. An air motor has no thermal cut-out and no duty-cycle rating, so it can be loaded to a stall and run continuously, where a universal-motor electric grinder overheats. Air tools also tolerate wet decks, washdown and confined spaces better, and avoid a trailing mains cable. Against that, a 115 mm electric grinder costs roughly a third as much and needs only a socket, so for light intermittent workshop use the electric tool is the better buy.
Do Trelawny angle grinders have IMPA codes?
Yes, for two models. The 4" 170.4050 is IMPA 59.03.01 and the Low Vibration 7" 170.4071 is IMPA 59.03.02. Trelawny publishes no IMPA code for the 4" with wire brush head (170.4150) or the Low Vibration 5" (170.4054).
Can you use the same discs on all Trelawny angle grinders?
No. The spindle threads differ: M10 on the 4", M14 on the 5" and 5/8" UNC on the 7". Discs and wire brushes are specific to each model - 491.4050 for the 4", 491.4055 for the 5", 491.4070 for the 7".
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