Skip to product information
1 of 3

RS185 - 18 Litre

RS185 - 18 Litre


Knapsack sprayer with 6 BAR maximum pressure & FPM seals for the spraying of mild acidic and neutral chemical solutions.
Regular price £126.50 GBP
Regular price Sale price £126.50 GBP
Sale Sold out
View full details

Collapsible content

Product Description

This knapsack sprayer is manufactured with a rigid polypropylene tank and fitted with FPM chemical resistant seals which will allow you to spray acidic and neutral chemical products. Due to the unique design of our RS range, the tank can be pressurised to 6 BAR (88psi) which is double the working pressure of the vast majority of other sprayers.

The potentially high working pressure means that there is not the requirement to constantly pump this sprayer in order to maintain a spray pattern. This is very useful, especially when using with our long telescopic lances.

Product Description

Special features of the product:

• Ergonomically formed shut-off valve with control pressure gauge

• Filling cap with integrated measuring cup and captive loop

• Large base: Safe stand even on an uneven surface

• Extra-large filling opening

• Ergonomically shaped integral grip that is adjustable in length

• Pump lever can be installed on left or right side

• Functional reliable spray wand holder

• Practical mounting bracket for spray shield on both sides

A review of the RS knapsack sprayers can be found in the 'Our Review' section. Simply click the tab above to read our review of the RS range of sprayers which, in addition to this sprayer, includes our 12-litre model and our brand new 18-litre model for alkaline solutions.

Whilst this prayer is fitted with FPM seals it does not mean that it can be used to spray all types of acidic chemical. We therefore recommend a compatibility test when using aggressive chemical solutions. If you think there may be an issue with a product that you wish to use then just send us the safety data sheet (MSDS) for the product and we will check compatibility and recommend an alternative sprayer if necessary.

Product Specification

  • Unit Height: 0.55m
  • Unit Weight: 5kg
  • Maximum Operating Pressure: 6 BAR (87 psi)
  • Tank Working Capacity: 18 litres
  • Total Tank Capacity: 20 litres
  • pH Range: 1-9*
  • Tank Material: Polypropylene
  • Tank Ullage: 2 litres
  • Pump: Plastic piston pump
  • Carry Position: Can be carried on back or by hand
  • Maximum Flow: 1.4 litres/min @ 6 BAR with supplied nozzle
  • Hose: 1.5 metres, reinforced with fabric insert
  • Lance: Brass, 50cm length and 360° rotatable
  • Supplied Nozzle: Brass, hollow cone 1.1 mm
  • Connector required when using with 3.2/5.4-metre telescopic lance
  • Padded shoulder carrying straps & back padding
  • 20 years spare parts supply GUARANTEED
  • Seals FPM - Synthetic rubber with high elasticity properties which makes
    it a very good product for the protection of seals and O-rings. FPM seals are highly resistant to hydrocarbons, oils, strong acids, aromatic and chlorinated solvents and has a high temperature resistance.

*We recommend a full compatibility test with aggressive chemical solutions. If you are unsure about a product that you plan to use then send us the safety data sheet (MSDS) for the product and we will check compatibility and recommend an alternative sprayer if necessary.

Resistance Guide

This will give you an indication of the chemical resistance of this sprayer. Next to each item you will see either YES (resistant), CON (conditionally resistant) or NO (unsuitable). This is only a guide but if you can't see the chemical you plan to use or have any questions then please just contact us.


  • Acetic Acid (maximum 10%): NO
  • Silicic Acid: YES
  • Peracetic Acid (maximum 6%): YES
  • Phosphoric Acid (maximum 30%): YES
  • Nitric Acid (maximum 10%): CON
  • Hydrochloric Acid (maximum 10%): CON
  • Aulphuric Acid (40%): CON


  • Butanol: CON
  • Ethanol: NO
  • Methanol: NO
  • Isobutanol: YES
  • Isporopanol: YES

Aliphatic Hydrocarbons

  • Decane: CON
  • N-Heptane: CON
  • N-Butane: CON

Aromatic Hydrocarbons

  • Naphtha: YES
  • Toluol (maximum 40%): YES
  • Xylene: YES
  • Heptaphene: YES


  • Diesel: YES
  • Kerosene: YES
  • Mineral Oil: YES
  • Petroleum Spirit: NO
  • Concrete Release Agent: YES


  • Acetone: NO
  • Ammonia: NO
  • Sodium Carbonate: YES
  • Sodium Hydroxide (maximum 30%): NO
  • Potassium Hydroxide: NO
  • Sodium Hypochorite (maximum 12.5%): CON


  • Weed Control: YES
  • Moss KIller: CON
  • Forestry: CON
  • Release Agents: CON
  • Lawn Care: YES

RS18 Product Booklet (pdf)


Can this sprayer be used with all types of acidic chemicals?

Although fitted with FPM seals, we can't guarantee that this sprayer is compatible with any type of liquid just because it's an acid. Please remember that it is not just the pH that determines which sprayer can be used but the active ingredients of your chemical. We therefore recommend that if there is any uncertainty then send us the safety data sheet (MSDS) for the product you wish to use and we will check compatibility. If the product is not compatible then we will recommend an alternative sprayer for you.

What does Tank Ullage mean?

Ullage is the name given to the gap between the maximum fill and the total tank capacity. It is important with sprayers as the larger the ullage is then the more space there is for compressed air. The more compressed air you have then the longer spraying time you have before you run out of pressure. Given the design of a knapsack sprayer the ullage is not as important as with a compression sprayer which is why, generally, knapsack sprayers will have a smaller ullage to tank capacity ration than a compression sprayer.

Can this sprayer be used with your long telescopic lances?

Yes. This sprayer can be used with both our 2.5 metre, 3.2 metre and 5.4-metre telescopic lances. We have included these lances in the accessories list and they include any required connectors. It can also be used with our shorter, telescopic brass lance extensions so additional reach isn't something that you really have to worry about.

What guarantee do I get with this sprayer?

You get a full 12 months with mechanical breakdowns so, providing that the sprayer is being used as intended, then if something snaps you tell us and we replace the part for you. If it's damage caused by a chemical compatibility issue then we will cover the damage providing that we have confirmed the chemical compatibility with the sprayer. When it comes to the availability of spares, this is guaranteed for 20 years from the date of purchase.

Our Review


The Mesto RS185 is a backpack sprayer with a 18-litre capacity, a white polypropylene tank and a 6 BAR maximum spraying pressure which gives a maximum flow rate of 1.4 litres per minute with the supplied nozzle.

Initial Impressions, Packaging and Sprayer Manual

Once you have purchased the sprayer, I suppose that the first thing that you see is the box and the box for the Mesto RS185 knapsack sprayer gave me a good first impression. It is brightly coloured with plenty of good quality and informative photos and with a construction that felt strong enough to both hold and give protection to the sprayer.

Upon opening the sprayer box, the first thing I found was an instruction manual and quite some instruction manual it is; over 125 pages of instructions and pictures. Okay, so only 8 of the pages are in English (as you can see a copy in our downloads section) but it is nice to get an instruction manual and this one tells you pretty much everything that you need to know, from a welcome message and safety notices through technical information, assembly instructions, care and maintenance information and a faults guide. Putting the manual to one side for a moment it was time to have a look at the sprayer. Everything was nicely packed around the tank so to remove the sprayer from the box required just removing the sprayer hose; with a gentle pull on the handle, the tank lifted easily from the box. My first impression of the sprayer is that it felt substantial and looked good as did the hose and various handles and metal lance. The next step is to assemble it.

Sprayer Assembly

I had a skim through the manual and everything seems straightforward enough. One of the very handy things with this sprayer is that the shoulder straps are already fitted to the tank, you only have to clip the bottom rings in place, so there are only five parts to put together. How hard can this be? Not hard at all, especially when you realise that there is a plastic bag inside the sprayer that holds a couple of small fittings. Please don’t forget these as you can’t assemble parts of the sprayer without them.

The first thing I did was to attach the hose to the handle and tank. Remember to slip the locking threads onto the hose before doing this. The 1.5-metre hose looks and feels like it could take some real battering. I think that it has a much sturdier feel than many hoses that I have seen with sprayers and matches the overall impression I have of the sprayer itself. I fitted the hose to the sprayer handle in a matter of seconds, but I did find pushing the hose onto the tank fitting to be a little tricky. However, a few extra seconds of pushing and the sprayer hose slipped into place. If you find the hose a little hard to push onto the fittings, then softening the ends of the hose by dipping them into hot water for a few seconds will help. The metal lance is then fitted to the handle and assembly is nearly finished. The only thing left to do is to fit the pump lever. This can be fitted to either the left or right side of the tank (for left or right-handed people) and it comes in two pieces with a small extension that is pushed into the main pump lever and allows the lever to be set at a length that best suits the operator with three options to choose from. The main pump lever is fitted to the tank by simply pushing it into a hole at the base of the tank and fitting a locking pin. Once again, you also have a choice of three settings giving you a width to suit the operator. I found this locking pin a bit of a pain to fit but that was mainly because I was trying to do it in very poor light. Once I had moved, so that I could see something, I managed to line up the holes and the pin slipped into place.

Assembly only took a couple of minutes. Obviously, I have put sprayers together before, but I have found the RS range of knapsack sprayers to be some of the easiest I have done especially as the shoulder straps are already done for you and the manual is there to help although I found the drawings easier than the written instructions. However, please note that the hose collars and pump lever locking nut are in the filling filter (for safety during transport) so you will have to open the yellow lid to find them.

Sprayer Use

The tank has a 140mm wide neck which makes filling easy. The bright yellow lid was easy to open and close and there is a plastic filter, in the neck, which I found easy to remove if not needed. I would, however, recommend leaving it in place so that nothing can be added to the tank that could block the nozzle when spraying. So, with tank filled I put the sprayer onto my back and with padded shoulder straps I thought the sprayer was very comfortable and sat well. Just a little word of advice, the straps need to be clipped to the base of the tank before you can wear it. There is plenty of adjustment in the straps, so all shapes and sizes should be well accommodated.

All that was left was to do some spraying. A few gentle movements of the pump lever and you can see the pressure gauge on the trigger handle start to rise. I like the pressure gauge. I think it’s a great touch, looks good and is helpful, letting you know when the 6 BAR maximum pressure has been reached. Pull the trigger and you are spraying.