How it works

The problem. The patent describes how cement-based roof coatings were usually applied in the early 1960s: a crew mixed the material on the ground, loaded it into bucket elevators, hauled it up to the roof, and two or more men spread it with swabs and buckets. Alex Jutila's aim, in the patent's words, was a mechanism with which "one man can perform an entire roof coating operation."

The answer. The Jetspray was one self-contained unit: a gasoline engine, a mixing tank with a slowly turning agitator, a positive-displacement pump and a single long hose. The coating stayed mixed in the tank, was pumped up to the roof, and was sprayed without compressed air (hence "airless"). Anything the hose didn't take went back into the tank through a spring-loaded relief valve, so the pump could run against a closed gun without damage.

One engine drives everything through two V-belts. A V-Plex friction clutch on the engine shaft slips at idle and grips as the governor speeds the engine up. Its belt (J) turns the 12 in pump pulley (I) on a short jack shaft (G), which turns the pump through a Gerbing G-100 jaw coupling with a rubber spider. Bob Ruth's notes and the leaflet call it a "universal coupling" (H). A small pulley on the outer end of the jack shaft drives a second belt (D) up to the 18 in pressed-steel pulley (C) on the agitator shaft. The patent describes the same arrangement: pulleys 42 and 44 on drive shaft 13, with belt 45 going to pulley 47 on the agitator shaft.

U.S. Patent 3,203,631, "Abrasive Type Roof Coating Apparatus." Alex O. Jutila, 5062 Zion, San Diego. Filed May 18, 1964 (Ser. No. 368,155) and issued August 31, 1965, with 3 claims in class 239-124. The attorneys were Hansen and Lane and the primary examiner was Everett W. Kirby. Download the patent (PDF).

The patent covers the problem of abrasive, cementitious coatings: mixtures of liquid with Portland cement or similar aggregate, applied over gravel roofs or mineral-surfaced cap sheet. If such a mixture is left still, the heavy particles settle out. If it is pumped, they pack into the outlet and choke it. The patent's answer is a set of parts that work together. That is typical of mechanical patents of the period: the individual parts (tanks, paddle agitators, helical pumps, by-pass valves) were already known, and what the claims protect is the combination.

What the three claims cover, in plain English

All three claims describe a "single line applicator" with these features in common:

• a tank with a cylindrical (half-round) bottom, with an agitator turning on the axis of that half-round;
• a flexible wiper blade on the agitator that reaches out and actually touches the curved bottom;
• a discharge line from the bottom of the tank, placed in the path of the wiper, with a grating over its inlet that the wiper sweeps on every turn;
• a pump fed from that line, with one power source driving both the pump and the agitator;
• one hose long enough to reach every part of the roof, ending in a nozzle with a valve to control it;
• a spring-biased valve that sets the pressure at which material flows from the pump to the nozzle.

Claim 1 is the most specific. It calls for several agitator blades, each set slightly clear of the bottom and each carrying its own wiper. It also requires that the spring valve sit in a by-pass line next to the pump discharge that returns material to the tank. Claim 2 is broader. It needs only a single wiper and "spring biased valve means" for controlling pressure, without describing the by-pass. Claim 3 adds the perforated shelf at the top of the tank, which receives and supports a bag of abrasive while it is slit open and emptied into the liquid.

The production tank is a long open trough. Its end plates are a "U" or "D" shape: straight sides at the top that blend into a semicircular bottom, with a curved weld seam visible in the shop Polaroids. The top edge is folded into a lip, and the leg braces are riveted through that lip with 1/4 in rivets, heads inside and tails "mushroomed" with a mallet (Bob Ruth's notes p. 11; instructions p. 9). A flat lid with turned-down edges hinges along the back and closes with two draw latches.

The agitator turns on the centreline of the half-round, so every blade passes the same distance from the curved floor. That geometry is what lets the wipers work.

Engine. A horizontal-shaft Briggs & Stratton. The July 1966 price list and the 4 HP mailers specify 4 HP. Bob Ruth's notes (p. 24), a Polaroid decal and the 1977 pump manual cover all say 5 HP. The manual cover records "5 HP Briggs and Stratton Eng S/N 130202 Model # 001501 Horizontal". Speed is set by the governor control (Z). The leaflet says to raise it "approximately 1/2 inch" to start and that "volume output is determined by pump r.p.m."

Clutch. The V-Plex friction clutch mounts on the crankshaft with a 3/16 in key and two set screws. Bob Ruth's notes say to file its outside edge so it doesn't chew the belt and to spray WD-40 on its internal spring (p. 25). At idle it slips, and when the engine is speeded up it grips and the pump starts ("Increase engine speed to engage friction clutch (Q), which starts pump"). The belt should "seat 1/2 way up clutch" (notes p. 26).

Jack shaft and coupling. 3/4 in shaft on pillow blocks shimmed with 3–5 washers, with the thrust collar toward the pump (notes p. 21). The 12 in cast-iron, six-spoke pulley mounts on a 3/4 in bore bushing. Alignment was taken seriously: the pump had to be "SQUARE!" to the engine or it would "cause extreme belt wear" (notes p. 19).

Agitator drive. TRU-RUN (Gates) steel hub 37866 (1 in bore) and rim 37776 make up the big pulley on the agitator shaft; a 1-3/4 in TRU-RUN steel pulley, no. 37322, goes on the jack shaft, and the belt is aligned "until belt runs true" (notes pp. 30–31). The 18 in pulley itself is a white pressed-steel disc on a threaded wheel hub (R), behind a drum-shaped guard (Y) with an expanded-metal face.

The brochures call it a "helical gear pump", a "helical pump" (1966 price list), a "rotor-stator" pump and, in the later tan brochure, the "ROTOSTATOR." The patent's version is "a well known helical rotor type with resilient housing." The family papers identify it exactly: a Robbins & Myers Moyno progressing-cavity pump. A 1977 Robbins & Myers manual, Operation – Assembly Instructions and Parts List for "L3" Drive End, is annotated by hand: "2L3 Rotor = 13.125 — Standard" and "3L3 Rotor = 18.250 — Heavy Duty."

The manual explains the frame code. The first digit is the number of stages, the letter is the model, and the last digit is the size of the pumping elements. A 2L3 therefore has two stages of size-3 elements, and a 3L3 has three stages, with a longer rotor, 18-1/4 in instead of 13-1/8 in. Each stage is one more sealed cavity between suction and discharge, so a longer, multi-stage element can generally hold more pressure. That explains the "heavy duty" note.

How a single helix pumps

The rotor is a hard steel single helix, like a twisted round bar. The stator is a moulded rubber lining (Buna-N in standard Moyno construction) with a double internal helix of twice the rotor's pitch. Cut across anywhere along its length, the stator's bore is a slot (two semicircles joined by straight sides) and the rotor is a circle. As the shaft turns, the rotor rolls eccentrically inside the slot, sliding from one end of it to the other. Along the length, the rotor and stator touch on continuous seal lines, so they enclose a chain of separate cavities that travel steadily from suction to discharge. The manual adds that as one cavity shrinks, the opposite one grows "at exactly the same rate," which gives an almost pulse-free flow with no valves.

For a roof-coating machine this suited the job well. Gritty, fibred or cement-laden coatings pass through without check valves to foul, the rubber stator tolerates abrasives better than close metal clearances would, and the output is proportional to shaft speed. That is why the leaflet can say volume is set by engine rpm.

How it was installed

Bob Ruth's notes (pp. 16–18, 23) set out the installation. Spacers go under the pump feet and are bolted to the tank brace with four 3/8 × 2 in bolts, left loose at first. The pump bolts to a 1-1/2 in companion flange with 1/2 × 2 in bolts and a rubber gasket. The pump is rotated "to insure a straight flow from tank to pump." The stator clamps ("caps") are tightened evenly because a cap "could break with more tension." Keystone No-Weld anti-seize goes on the pump shaft, and the shaft key is a 1-3/4 × 3/16 in piece filed and bevelled for an easy fit. The shop instructions add that the pump's grease fitting faces up once it is in place, and that the key taped to the new pump's shaft was reused for the engine clutch.

The patent only calls for "spring biased valve means." In the shop that turned into a clever bit of plumbing made from standard pipe fittings, a stainless ball and a bolt. Bob Ruth's notes describe the procedure twice, in pencil (pp. 40–46) and in a neat block-capital version headed "PRESS. ADJ. VALVE" (pp. 3–4 and 50). The printed leaflet gives the finished assembly part numbers 24–38, which are used in the drawing below.

Pump pressure acts up through the bore of the 8 in nipple on the underside of the ball. When that force beats the spring, the ball lifts and coating squeezes around it and out of the tee's side branch, straight back into the tank. Screwing the bolt down compresses the spring and raises the relief pressure. The operator sets it while watching the gauge (O).

Our reading of the design (interpretation, not stated in the notes):

• The 1 in run of the tee is on the seat side for a reason. A 1 in fitting's bore (about 1.05 in) leaves an annulus around the 7/8 in ball for the returning coating to pass through. The nipple, threaded through the shortened bushing, puts the seat right inside that larger bore.
• The pinned nut and the 3/16 in head gap look like a pair of stops. The bolt can travel only between the head bottoming on the bushing (maximum spring load) and the nut hitting the bushing's underside (minimum). With 14 threads per inch, 3/16 in is about 2-5/8 turns. The pin also means the bolt can't be unscrewed out of a pressurised valve.
• Steps 8 and p. 46 ("loosen adjustment bolt and check for end play … a small rattle") then set the range. At the loosest position the ball must have a little free play, so the valve can be fully released to flush debris (leaflet, step 4b). At the tightest, the spring must not go solid.

The power that ends up in the fluid is flow times pressure. In US units, hydraulic horsepower = gpm × psi ÷ 1714. Applying that to the advertised figures:

The 6–7 gpm, 200–250 psi ratings call for one or two horsepower at the pump shaft. With agitator and belt losses added, they sit comfortably within a 4–5 HP engine. The tan brochure's "up to 1,000 lbs. with heavier coatings" cannot happen at the same time as its "up to 7 gpm". That combination needs more power than the engine has, so 1,000 psi could only apply at a much lower flow. The documents don't say whether the 2L3 elements were rated that high. We suspect the figure refers to a short-term pressure capability rather than a working point, but that is a guess.

From the printed Service and Operating Instructions leaflet (letters refer to its photographs), with the patent's description of the same cycle.

Leaflet warning: "do not run pump when dry. Prime pump and hose before putting coating into machine."

To start

1. Check oil, lubrication and gas in the engine.
2. Release the tension on the pressure adjustment valve (S).
3. Attach the hose and spray gun to the outlet valve (X). Put the gun's nozzle back into the tank and open X so everything circulates freely. Make sure the tank has the correct solvent.
4. Raise the governor adjustment (Z) about 1/2 in, pull out the choke, and start.

To operate

1. Speed up the engine to engage the friction clutch (Q); this starts the pump. Set engine speed for the output wanted.
2. Set the pressure adjustment valve (S) while watching the gauge (O).

Mixing and spraying

• Pour in a compatible solvent first, then the coating. The machine mixes it "to uniform texture" while it recirculates. When it is mixed, shut X, set S to the working pressure, and spray.
• Coating can be added without stopping the machine.
• The patent describes the cement version of the same cycle. With the main cock closed, pour in water, set a bag of Portland cement on the loading screen, cut it open with a shovel and let it fall through into the liquid. The patent also names "Alumination 301" (Republic Powdered Metals Co.) as a suitable coating.
• Spray pattern is set by the nozzle. Volume is set by the by-pass spring and the engine speed (patent).

When it clogs

• Gun stops spraying: debris in the nozzle. Close X, remove the nozzle and clean it.
• Debris in the relief-valve seat: release all tension on S and close X. The free return flow through S will wash the obstruction out.
• Asphalt-base coatings thicken in the cold; thin them with compatible solvent. For heavy or fibred coatings, remove the outlet screen in the tank.

Cleaning

• Clean thoroughly after every day's use. Drain the tank, clean with solvent, then run water through the tank, pump and hose to flush out all solvent (leaflet).
• The patent adds two details. Keep the engine running while draining so the aggregate doesn't settle. During the water flush, close the gun valve from time to time so the cleaning liquid also flushes the by-pass line and pressure valve.

The sales literature changed over the years, and the documents genuinely disagree. Only two pieces carry a date: the July 1966 price list and the "New 1967 Model" mailer. The others are listed roughly in the order their content suggests. The early pieces give the 2223 El Cajon Blvd. address and the later tan brochure gives 6308 Riverdale St. Highlighted cells are where a figure changes.

Other sources: Bob Ruth's assembly notes (p. 24) and a 1977 Robbins & Myers manual annotation both say 5 HP Briggs & Stratton. An undated letter signed by David Eliason, Sales Manager, extends the guarantee "to 90 days" and adds "three different size screens and nozzles". That conflicts with the one-year guarantee in the mailers, so it is probably an earlier letter, but it is undated. The patent prototype held 60–75 gal.

No Jetspray machine is known to survive, and no factory drawings have been found. The 3D model and the drawings on this page were rebuilt from the documents, and every dimension is kept in one file (cad/spec.py, published as /data/spec.json) with its status and source:

• documented stated in a period document (cited);
• derived calculated from documented values (method cited);
• estimated judged from photographs and proportions; open to correction.

If you have a Jetspray part, photograph or measurement that pins down an estimated value, the family would love to hear from you.

The citing patents cover a wide range: cement and mortar, refractory and ceramic slurries, battery paste, hydro-seeding, agricultural chemicals and aircraft cleaning. The common thread is the problem the Jetspray solved, which is keeping a heavy, settling mixture stirred and pumping it out of the bottom of a tank without clogging.