Alkaline Backpack - 18 litre

Resistant to most alkaline cleaning chemicals. 18 litre capacity tank with 6 bar maximum working pressure.

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Product code


Each £110·00 exc VAT
Total £110·00 exc VAT
Total £132·00 inc VAT

This knapsack sprayer is manufactured with a rigid polypropylene tank and fitted with EPDM chemical resistant seals which will allow you to spray alkaline 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.

Special features of the RS185M sprayer:

  • Ergonomically formed shut-off valve
  • EPDM seals giving high resistance to base products
  • Filling cap with integrated measuring cup and captive loop
  • Large base giving a safe footing even on an uneven surface
  • Extra large opening for easy filling
  • Compression pump lever can be installed on left or right side

(Note: The alkaline model does not have a pressure gauge due to chemical compatability)

A review of this RS knapsack sprayers can be found in the 'Our Review' section, simply click the tab to read our review of the knapsack sprayer. We also have the 12-litre capacity backpack sprayer and our 18-litre model, both of which are fitted with FPM seals for protection against acidic products.


  • Unit Height: 0.55m (maximum)
  • Unit Weight: 5kg (when empty) 16.5kg (gross maximum weight)
  • Maximum Operating Pressure: 6 BAR (87 psi)
  • Tank Working Capacity: 18 litres
  • Tank Material: Polypropylene
  • Carry Position: Back
  • Maximum Flow: 1.4 litres/min @ 6 BAR
  • Hose Length: 1.5-metres
  • Lance: 500mm, chemical resistant
  • Nozzle: Flat jet, chemical resistant
  • Padded shoulder carrying straps & back padding
  • 20 years spare parts supply GUARANTEED
  • Seals EPDM that are resistant to solvents and is mainly resistant to base products (alkalines). Generally, EPDM does not have a high resistance to polycarbon based oils and to fuels.


The Mesto RS185M has an 18-litre capacity white, polypropylene tank and with a 6 BAR maximum spraying pressure which gives a maximum flow rate of 1.4 litres per minute.

Initial Impressions, Packaging, and Sprayer Manual

Upon opening the sprayer box, the first thing I find is an instruction manual. Quite some instruction manual it is too; over 125 pages of instructions and pictures. Okay, so only 8 of the pages are in English but it is still nice to get an instruction manual. As this is a brand new model, you also get an extra couple of pages in addition to the manual. These give an outline of the EPDM seals and how the sprayer can be used which is, obviously, different to the other sprayers within the RS range that are fitted with FPM seals for acidic chemiacls. The manual tells you pretty much everything 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's time to have a look at the sprayer. Everything is nicely packed around the tank so removing the sprayer from the box simply requires removing the sprayer hose and with a gentle pull on the handle, the tank lifts easily from the box. My first impression of the sprayer is that it feels substantial and looks good. Likewise the hose and various handles and plastic lance. The next step is to assemble it.

Sprayer Assembly

I have a skim through the manual and everything seems straightforward enough. The shoulder straps are already fitted to the tank so there are only five parts to put together. How hard could it 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 do is 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. It has a much sturdier feel than many hoses that I have seen with other sprayers, and my impression of the hose matches my overall impression of the sprayer itself. I fit the hose to the sprayer handle in a matter of seconds, but I do find pushing the hose onto the tank fitting to be a little tricky. However, a few extra seconds of pushing and the sprayer hose slips into place. If you find the hose a little hard to push onto the fittings, 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 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 find this locking pin a bit of a pain to fit, but that is mainly because I am trying to do it in very poor light. Once I move so that I can see something, I manage to line up the holes and the securing pin slips into place.

Assembly only takes 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. The manual is there to help, although I found the drawings easier than the written instructions.

Sprayer Use

The tank has a 140mm wide neck which makes filling easy. The bright yellow lid is easy to open and close, and there is a plastic filter in the neck which I find 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 the tank filled, I put the sprayer onto my back. The padded shoulder straps ensure that the sprayer is very comfortable and sits 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 is left is to do some spraying. Pull the trigger and you are spraying.

This knapsack sprayer can be used with our 3.2-metre & 5.4-metre telescopic lance extensions. All you need is one of the connectors which will join the lance handle to the extension handle. I have used this sprayer with the telescopic lance and have found it easy to connect. TIP: I found that locking the trigger of the telescopic lance in the on position and using the sprayer handle to regulate liquid flow the easiest way to spray.

I notice that this sprayer can work up to 6 BAR. Do I need this much pressure?

How much pressure you need to use, depends upon where you are spraying and the products you are using. Many products around the home and garden can be easily applied with only 3 BAR however if the liquid is thicker then you will need more pressure. Just because the sprayer can work up to 6 BAR, you don't have to use it at this pressure.

Can I change the side that the compression handle is fitted?

Yes, the handle can be easily moved from one side to the other. It takes a couple of minutes and should be done when the tank is empty of liquid.

This sprayer can handle alkaline chemicals, can I also use it for acids?

This sprayer is fitted with EPDM seals which have very high resistance to base (alkaline) products as pH neutral and some, very weak, acidic solutions. If you want to use strong acidic chemicals then we would recommend our Acid Cleaner sprayer.

Are the shoulder straps easy to fit?

The straps are very, very easy to fit as the sprayer is supplied with the straps already fitted for you. There is no fiddling around, just open the box and the sprayer is ready to put on.

What is the '5-metre hose & handle' in the purchase options?

As our RS range of knapsack sprayers can be fully compressed meaning that you don't have to pump to spray, many customers like to take advantage of the massive 6 bar air capacity and leave the tank on the floor whilst climbing a ladder to spray. This 5-metre hose allows you to pump the tank then not have to carry it around to spray. It can be left on the floor whilst you climb a ladder or just walk around. The hose allows to you be up to 5-metres from the tank.

"I have ordered your bundle pack B Alkaline Backpack 18 litre - Sprayer together with 5.4-metre telescopic lance and connector. I would like to say thank you to Lee who gave me a lot of product information and advice on how to connect and use the product" Mr Sondhi, Coventry