Sprayer Troubleshooter and Seal Finder
Most sprayer faults come from a few small parts: the O rings and seals, the pump, the valves, the hose and the nozzle. A sprayer that leaks or will not hold pressure usually needs cleaning, grease or a seal kit, not a new sprayer. Seals that swell, go soft or crack can mean the seal does not suit the chemical: VITON (FKM) and EPDM suit different chemicals. Pick your sprayer and the problem below to get the likely causes in order, the checks and the fix. Then check your chemical in the seal finder.
Safety first. Release the pressure before you open a sprayer, rinse it before you repair it, and wear the gloves and eye protection the SDS lists. Never use a pesticide sprayer for anything else. The chemical label and the SDS always come first.
Free tool
Find the fault, then the right seal
Pick your sprayer and what it is doing. You get the likely causes in order, the checks to do and the fix. The seal finder then checks your chemical against our Chemical Compatibility Guide.
Loading the troubleshooter. It needs JavaScript; the common problems, the seal table and the worked examples below work without it.
A guide only. The chemical label, the SDS and your sprayer's manual come first. Release the pressure before you open a sprayer, rinse it before you repair it, and wear the protection the SDS lists. Seal answers come from the NORA PRO Chemical Compatibility Guide and depend on the exact product, its strength, the temperature and how long it stays in the sprayer.
Common sprayer problems and fixes
For a pump up pressure sprayer unless the problem says otherwise. The troubleshooter above has every problem for trigger bottles, pump up sprayers, knapsacks and pump up foamers, with the checks for each cause and where each step comes from.
| Problem | Likely causes, most likely first | First thing to try |
|---|---|---|
| Will not build pressure | The head or cap is not screwed on tight; the pump piston O ring is dry or worn; a valve in the pump is dirty, worn or out of place | Release the pressure, start the thread square and tighten the head by hand. |
| Builds pressure, then loses it | The pump piston O ring is dry or worn; the seal under the head is worn, twisted or missing; the head or cap is not screwed on tight | Grease the O ring with the lubricant your sprayer’s manual names. On EPDM seals use silicone oil only: petroleum based grease swells EPDM. |
| Leaks or drips at the trigger valve or nozzle | The trigger valve’s O rings are dry or worn; there is air in the hose and lance; the nozzle is blocked, worn or missing its insert | Take the valve apart and grease its O rings. Replace worn O rings, or the whole valve. |
| Leaks at the pump or the top of the tank | The head or cap is not screwed on tight; the seal under the head is worn, twisted or missing; the pressure relief valve is dirty or its O ring is worn | Release the pressure, start the thread square and tighten the head by hand. |
| Leaks at the hose or lance | A hose or lance connection is loose, or its seal is worn; the hose is worn or damaged; the seals do not suit the chemical | Tighten the coupling nut, then test it with water under pressure. |
| Sprays unevenly, drips or clogs | The nozzle is blocked, worn or missing its insert; a filter is blocked; the pressure has dropped as you spray | Unscrew the nozzle cap and clean the nozzle with clean water and a soft brush, or with compressed air. Never use a hard object, never tap it on a hard surface, and never blow through it with your mouth. |
| Seals swollen, soft or cracked | The seals do not suit the chemical; chemical was left standing in the sprayer; petroleum based grease was used on EPDM seals | Fit new seals of the material that suits the chemical, or use a sprayer built for it. |
| Pump hard to push | The pump piston O ring is dry or worn; the pump cylinder or its moving parts are dirty or dry; chemical was left standing in the sprayer | Grease the O ring with the lubricant your sprayer’s manual names. On EPDM seals use silicone oil only: petroleum based grease swells EPDM. |
| Pressure drops fast as you spray (knapsack sprayer) | The pressure chamber is full of liquid; you are not pumping fast enough; a pump valve is dirty or worn | Spray or drain the tank completely empty, then pump with no liquid in it to fill the chamber with air again. |
| Hose or tank sucked in (collapsed) (knapsack sprayer) | Air cannot get back into the tank; the intake is blocked; the hose is worn or damaged | Clean the vent hole. Replace a cap with no vent with the right vented cap. |
| Foams poorly, sprays unevenly or clogs (pump up foam sprayer) | The foam pad in the nozzle is clogged; the air holes at the foam nozzle are blocked; the pressure has dropped as you spray | Clean the foam pad with clean water and a soft brush, or replace it. |
| Will not spray, or only dribbles (trigger spray bottle) | The nozzle is blocked, worn or missing its insert; the suction tube is blocked; the trigger is worn or damaged | Unscrew the nozzle cap and clean the nozzle with clean water and a soft brush, or with compressed air. Never use a hard object, never tap it on a hard surface, and never blow through it with your mouth. |
| Leaks at the trigger or where it screws on (trigger spray bottle) | The trigger is loose on the bottle, or its seal is out of place; the trigger is worn or damaged; the trigger’s seals do not suit the chemical | Tighten the trigger by hand. If it still leaks, check the sealing surface and replace a damaged seal or the trigger. |
Before you take anything apart, release the pressure: pull the relief valve, or on a sprayer with no valve to pull, such as a Klager, unscrew the head slowly. After a repair, test the sprayer with clean water, and if it still leaks, do not use it.
VITON or EPDM: which seal for which chemical
VITON (FKM) and EPDM are the two seal rubbers in chemical sprayers, and they suit different chemicals. Our Chemical Compatibility Guide rates each chemical for three sprayer builds:
- Acid resistant sprayer: VITON seals, polypropylene pump, acid resistant springs.
- Solvent resistant sprayer: VITON seals, nylon pump, stainless steel springs.
- Alkaline resistant sprayer: EPDM seals, polypropylene pump, stainless steel springs.
EPDM is the wrong seal for petroleum solvents, for the same reason that petroleum based greases swell it. Here is what the guide says for some common chemicals:
| Chemical | Seal in our guide | Rating |
|---|---|---|
| Bleach (sodium hypochlorite) | EPDM, chlorine up to 12.5% | Suitable |
| Chlorine based sanitiser (hypochlorite) | EPDM, chlorine up to 12.5% | Conditional |
| Sodium hydroxide (caustic soda) | EPDM, up to 50% | Suitable |
| Potassium hydroxide (caustic potash) | EPDM, up to 30% | Suitable |
| Ammonia (liquid) | EPDM, up to 10% | Suitable |
| Strongly alkaline cleaner or degreaser (pH above 9.5) | EPDM | Suitable |
| Water based cleaner (rated by pH) | pH 7 or below: VITON (FKM). pH above 7 to 9.5: VITON (FKM) or EPDM. pH above 9.5: EPDM. | Depends on the strength |
| Hydrochloric acid | Up to 10%: VITON (FKM). 10 to 25%: VITON (FKM), conditional. Above 25%: ask us. | Depends on the strength |
| Sulphuric acid | Up to 10%: VITON (FKM). 10 to 30%: VITON (FKM), conditional. Above 30%: ask us. | Depends on the strength |
| Phosphoric acid | Up to 30%: VITON (FKM) or EPDM. Above 30%: ask us. | Depends on the strength |
| Citric acid | Up to 30%: VITON (FKM) or EPDM. Above 30%: ask us. | Depends on the strength |
| Acetic acid | Below 5%: ask us. 5 to 30%: EPDM, conditional. Above 30%: ask us. | Depends on the strength |
| Isopropyl alcohol (IPA) | VITON (FKM) or EPDM, up to 100% | Suitable |
| Diesel | VITON (FKM), up to 100% | Suitable |
| Petrol | VITON (FKM), up to 100% | Suitable |
| White spirit (mineral turps) | VITON (FKM), up to 100% | Suitable |
| Solvent degreaser (petroleum based) | VITON (FKM) | Suitable |
| Brake cleaner (petroleum solvent based) | VITON (FKM) | Suitable |
| Herbicide, pesticide and plant protection products (water based) | EPDM | Conditional |
| Acetone | Ask us: not rated | Ask us |
| Hydrogen peroxide | Ask us: not rated | Ask us |
| Quaternary ammonium sanitiser (quat) | Ask us: not rated | Ask us |
Guidance only. Compatibility depends on the exact product, its strength, the temperature and how long it stays in the sprayer. Check the Safety Data Sheet (SDS) and ask us before you buy. Klager operating instructions (02/2026): do not fill liquids hotter than 30 °C into its sprayers. Ask us about warmer liquids. The seal finder gives the answer for your strength, says when it changes with oils or solvents in the product, and lists the sources.
Why seals swell, go soft or crack
- The seals do not suit the chemical. Chemicals can damage the seals inside a sprayer. VITON (FKM) and EPDM seals suit different chemicals, so the seal should match what you spray. Petroleum based greases swell EPDM and destroy it, which is the same reason EPDM is the wrong seal for petroleum solvents. A stronger mix than the chemical maker gives also shortens the life of a sprayer.
- Chemical was left standing in the sprayer. Chemical left in a sprayer works on the seals for days. Rinsing after every use gives them the longest life.
- Petroleum based grease was used on EPDM seals. Petroleum based greases swell EPDM and destroy it.
- Heat, sun, frost or age. Seals dry out with age, and heat, sun and frost damage sprayers. UV turns a sound bottle brittle.
New seals of the same material will fail the same way if the chemical is the cause, so check the chemical before you buy a seal kit.
Worked example: a pump up sprayer that will not hold pressure
A cleaner fills a pump up sprayer with a strongly alkaline degreaser and pumps it up. By the next morning it is flat. In the troubleshooter: pump up pressure sprayer, then builds pressure, then loses it. The causes come in this order:
- The pump piston O ring is dry or worn. Release the pressure, take the pump out and look at the O ring on the piston: smooth, whole and lightly greased. Grease the O ring with the lubricant your sprayer’s manual names. On EPDM seals use silicone oil only: petroleum based grease swells EPDM.
- The seal under the head is worn, twisted or missing. Release the pressure, take the head off and look at the seal: flat, whole and sitting right. Seat the seal straight and grease it lightly. Replace it if it is damaged.
- The head or cap is not screwed on tight. Check the head sits square on the tank and is screwed on hand tight. Release the pressure, start the thread square and tighten the head by hand.
The O ring on the pump piston is flat and dry, so it needs a new seal set. In the seal finder, a strongly alkaline cleaner or degreaser (pH above 9.5) with no oils or solvents gives EPDM (suitable): alkaline resistant sprayer. For a Klager sprayer that is the EPDM Seals Kit, which our product page lists for the Klager 1.2L Alkaline Resistant. Grease the new O ring with silicone oil only, because it is EPDM.
Worked example: swollen seals after a solvent degreaser
A workshop uses its alkaline resistant (EPDM) sprayer for a petroleum based solvent degreaser. After a week the seals are swollen and it leaks at the pump. In the troubleshooter: pump up pressure sprayer, then seals swollen, soft or cracked. The first cause is the seals do not suit the chemical.
In the seal finder, solvent degreaser (petroleum based), with oils or solvents: yes, gives VITON (FKM) (suitable): the solvent resistant sprayer, such as the Klager 1.0L Solvent Resistant, Klager 1.5L Solvent Resistant, Klager 1.0L Superior Solvent Resistant. New EPDM seals would swell again. Keep the EPDM sprayer for alkaline cleaners, and use a VITON sealed solvent sprayer for the degreaser. When its seals wear, fit the VITON Seals Kit, which our product page lists for the Klager 1.0L and 1.5L Solvent Resistant, 1.2L and 1.5L Acid Resistant.
Looking after a sprayer so it lasts
- Mix only as much as you need. Where possible, pour what is left back into its own container; if not, dispose of it as the label or SDS says, never down the drain. Rinse the sprayer with clean water, spray some through the hose and nozzle, then empty it. Do not leave chemical standing in it.
- Grease the pump piston O ring each time you clean it down, with the lubricant your manual names. On EPDM seals, silicone oil only.
- Mix in a separate container, dissolve powders fully, and pour the mix in through the filling strainer.
- Set the pump head down on a clean surface while you refill, so dirt does not block the nozzle.
- Do not leave a sprayer under pressure. Store it empty and depressurised, out of heat, frost and direct sun: liquid that freezes in it can damage it beyond repair.
More in our Refill and Maintenance Guide: how to refill a pressure sprayer, the pump strokes and pressures, and care after the job.
Parts and seal kits
We stock VITON and EPDM seal kits, pressure relief valves, triggers and pumps for the Klager and Gloria sprayers we carry. Each product page says which sprayers it fits, and the seal finder lists the parts with the right seal for your chemical, read from those pages. See all parts and seal repair kits, or ask us with your sprayer model and we will confirm the part.
Sources: repair steps from our Refill and Maintenance Guide and the makers’ own manuals and support pages, read on 19 October 2026: Solo (pressure sprayer seals, backpack troubleshooting, handheld troubleshooting and its manuals), GLORIA manuals, Birchmeier, Mesto and Klager, and the care guides Bravo Company wrote for the sprayers it sold before NORA PRO. Seal answers from our Chemical Compatibility Guide dataset (v2.0.3, reviewed 19/10/2026).
Frequently asked questions
Why is my pressure sprayer not building pressure?
Most often the pump is not sealing. Check the head is square and screwed on hand tight, then look at the O ring on the pump piston: grease it if it is dry, and replace it or fit a seal kit if it is worn. A dirty or worn valve at the bottom of the pump, or grit holding the pressure relief valve open, also stops it building pressure.
Why does my sprayer lose pressure?
Usually a worn pump piston O ring or a worn seal under the head. Check the head is square and hand tight, the bottle is not filled past the fill mark (it needs an air space to hold pressure), and grit is not holding the pressure relief valve open. On a knapsack, a pressure chamber full of liquid makes the pressure drop fast: pump it completely empty.
Why is my sprayer leaking?
Find where it leaks first. At the trigger valve or nozzle, it is usually the valve’s O rings or air in the line. At the top of the tank, a loose head or a worn head seal. At a hose, a loose coupling nut. Release the pressure before you undo anything, and if it still leaks after a repair, do not use it.
What is the difference between VITON and EPDM seals?
They are two seal rubbers that suit different chemicals. In our Chemical Compatibility Guide, VITON (FKM) is the seal of the acid resistant and solvent resistant sprayers, and EPDM is the seal of the alkaline resistant sprayer, which the guide rates for bleach and caustics. EPDM is the wrong seal for petroleum solvents. Check your chemical, its strength and the temperature in the guide.
Why are my sprayer seals swollen?
Often because the seal does not suit the chemical, because chemical was left standing in the sprayer, or because petroleum based grease was used on EPDM seals. Fit new seals that suit the chemical, rinse the sprayer after every use, and use silicone oil only on EPDM.
What grease should I use on sprayer seals?
The lubricant your sprayer’s manual names, because the makers differ. On EPDM seals use silicone oil only: petroleum based greases swell EPDM and destroy it. Grease the pump piston O ring each time you clean the sprayer down.
Can I fit a VITON seal kit to any sprayer?
Only a kit made for that sprayer. Each of our seal kit product pages says which sprayers it fits, and the seal finder shows that in the product page’s own words. Tell us your model and we will confirm the kit.
How do I clean a blocked sprayer nozzle?
Take it off and clean it with clean water and a soft brush, or with compressed air. Never use a hard object, never tap it on a hard surface, and never blow through it with your mouth. Check the swirl insert is in place. If the spray is still uneven, replace the nozzle, because nozzles wear.
How hot can the liquid in a sprayer be?
No hotter than your sprayer’s manual allows. Klager’s limit is 30 °C; the other makers we checked give 30 to 50 °C depending on the model. Heat and sun also damage seals and sprayers, so store it in the shade.
What if my chemical is not in the seal finder?
Then we do not guess. The seal finder only answers from our Chemical Compatibility Guide. Send us the SDS and your sprayer model and we will check it.