Chemical Will Not Draw Through the Injector

Why this matters

An injector that stops drawing does not always announce itself. The wand still sprays water, the machine still sounds normal, and unless the tech is watching the tank level or smelling for chemical, a full house wash can run start to finish as a plain water rinse with nothing actually killing the mildew that brought the customer in. The job comes back looking the same in a few weeks, and it reads to the customer as a bad clean rather than what it actually was, chemical that never left the tank. The other failure mode is worse: a tech who notices weak or no draw mid-job and "fixes" it by switching to a narrower tip or cranking the machine's pressure up, which does not solve an air leak or a clogged strainer and instead turns a chemical delivery problem into a surface-damage risk on whatever the wand is pointed at when the pressure changes.

Before touching the suction line, protect yourself first

The suction tube and the injector body both hold residual chemical even when nothing is spraying, and disconnecting a fitting to inspect it can release a drip or a fine mist of whatever concentration was last drawn through it. Eye protection and gloves go on before any fitting on the chemical side is loosened, the same PPE called out in the [Soft Wash Skid Setup and Tank Mixing] procedure, and the machine's trigger is locked off with the engine or pump not running before any suction-side fitting comes apart, so nothing pressurizes the line while a hand is on it.

Do not clear a suspected clog by blowing compressed shop air backward through the suction tube. It is a common shortcut and it is the wrong one: a line that still holds residual concentrate can spray that concentrate out the open tank end under air pressure it was never built to hold, reaching whoever is standing near the tank. Clear a suspected clog by disassembling the strainer or fitting and clearing it by hand, with the same PPE already on, and if the line will not come apart by hand, it gets replaced rather than forced.

The case: a house wash where nothing was drawing

Second stop of the day, downstream injector setup, correct black low-pressure tip already confirmed on the wand from the morning's setup check. The tech noticed the tank level had not moved after two minutes of spraying against the siding, no chemical smell at the surface, and no sign of the mix doing anything the water alone would not.

First check: the tip. The most common cause of a downstream injector losing draw, covered in [Downstream versus Upstream Injector Setup], is a high-pressure tip sitting where the low-pressure tip belongs. The tip on the wand was pulled and checked against its stamp: correctly the black 65-degree low-pressure tip, matching what the morning setup had confirmed. Ruled out.

Second check: the suction strainer. The strainer at the tank end of the suction tube, a small mesh filter that keeps tank sediment out of the injector, was pulled and inspected. It was partially clogged with a crust of dried residue, likely mineral buildup from a prior batch left to evaporate in the tube rather than rinsed out. The strainer was cleaned and reseated, and a clean-water draw test ran per the bucket method in the injector setup procedure: the injector's own rating called for pulling a quart in about 45 seconds, and this test came back at roughly 110 seconds, better than zero draw but still far off the rated time. A partially clogged strainer was a real contributor, but the numbers said it was not the whole story.

Third check, and the actual cause: a cracked suction fitting. With the strainer clean but draw still far under spec, the barbed fitting where the suction tube pushes onto the injector body got a close look and a wet-hand pass along its length. A hairline crack at the base of the barb, invisible at a glance, was pulling a faint hiss of air with the pump running. An air leak in a suction line beats a liquid draw every time, because air offers far less resistance to the injector's pressure differential than lifting chemical up several feet of tube does, so the injector was preferentially pulling air through the crack rather than pulling the tank's contents, which explains both the near-total failure with the strainer clogged and the still-poor result once that strainer was clear. The cracked fitting was replaced and resealed with a new clamp, and the draw test re-ran clean: a quart pulled in 47 seconds, inside the injector's rated range.

Why the checks ran in that order

The tip check came first because it is the single most common cause and takes seconds to rule in or out with no tools. The strainer came second because it is also fast, does not require breaking a sealed fitting, and clogging is a routine maintenance issue this system produces on its own over time. The suction fitting came last because confirming a hairline crack takes closer inspection and because ruling out the two faster, more common causes first is what turned a vague "no draw" into a specific number, 110 seconds against a 45-second rating, that made clear a real problem remained even after the strainer was addressed. Jumping straight to pulling fittings apart on the first job of the day would have cost more time for the same answer, and would have skipped the one number, the bucket-test time, that told the tech the strainer alone was not the fix.

What a full versus partial draw failure tells you

Total draw failure (zero tank movement, no measurable draw at all) points hardest at the tip or a fully blocked strainer, since either one removes the venturi's pressure differential or the suction path entirely. A partial draw failure that measures well under the injector's rated time, as in this case, points at a partial restriction (a partly clogged strainer) or a partial air leak, and the two can stack: a partially clogged strainer plus a hairline air crack are each capable of degrading draw on their own, so a fix that only addresses one still leaves a measurable, timed test short of spec, which is exactly the signal that sent this case to a third check rather than stopping at the strainer.

What changes the answer: an upstream system

Everything above assumes a downstream injector, the setup where tip choice governs whether the venturi effect exists at all. On a softwash skid running upstream metering into its own dedicated low-pressure pump, the tip on the wand is no longer a suspect, since that system meters chemical ahead of a pump that is not the belt-drive unit the wand's tip serves at all. The first check on an upstream system that will not draw is the metering valve itself, confirming it is actually open and set to something other than zero, which is a more common cause on that architecture than on a downstream one simply because there is a physical valve a hand can bump closed while loading gear onto a truck. From there the suspects converge with the downstream case: a clogged strainer, an air leak in the suction path, or the dedicated pump itself failing to prime, each checked and timed against its own rated draw the same way. The lesson carries across both architectures even though the first suspect changes: rule out the cheapest, most-bumped point of failure first, then work toward the ones that take a fitting apart to confirm.

What went on the ticket

The job record noted the actual cause, a cracked suction fitting, rather than a generic "injector serviced" line, because the next tech who pulls this rig needs to know a fitting was replaced, not guess at why draw was ever a problem. The two intermediate numbers, the 110-second partial-draw reading after the strainer alone was cleaned and the 47-second reading once the fitting was replaced, both went on the ticket as well. Recording only the final passing number would have buried the fact that the strainer clean was a real, necessary step and not a wasted one, which matters the next time this same rig shows a slow draw and someone has to decide how far back down this list to start.

Catching it before the job, not mid-spray

A pre-job bucket test, the same one used to verify a new setup in the [Downstream versus Upstream Injector Setup] procedure, catches every cause in this case before the truck ever leaves for the site: a wrong tip, a clogged strainer, or an air leak all show up as a slow or failed draw time against the injector's own rating, in a controlled test with a bucket rather than discovered halfway through a customer's siding. A suction line and strainer that get a visual and wet-hand check at the start of each week, the same interval called out for tip wear in the [Nozzle Tip Color and Spray Angle Reference], catches a developing crack or a building residue clog before it turns into a failed draw on a live job at all.

References

• See related: Downstream versus Upstream Injector Setup
• See related: Soft Wash Skid Setup and Tank Mixing
• See related: Nozzle Tip Color and Spray Angle Reference
• Manufacturer documentation for the specific injector's rated draw time and serviceable parts (strainer, check valve, suction fitting)