Accossato Brake Pump - GA model - 19 PRS

The humble master cylinder! an inherently simple device! Following this PFM, then came along and set the bar that bit higher with their three-bearing lever design, allowing the lever to roll on the piston plunger, reducing stiction and side loading from the piston, allowing for a large bore, small lever ratio design, giving the smoothest lever feel on the market... currently—and that is where the technology has remained for decades. I myself have wondered how the current state of the art could possibly be improved to no avail... does it even need to be?

Well, yes and no; the current standard does the job—however! Most people on track have suffered with brake issues, not all, but some come from the master cylinder—as mentioned above, stiction and side loading of the piston as the seals move up and down the bore create a mushy feel and reduce power transfer to the calipers, meaning more braking effort from the rider is required. As the brake fluid heats up, it becomes harder for the seals to hold pressure, creating (one of several reasons for) more lever travel. Seals swell when submerged in brake fluid, which varies for different fluid and seal materials, and means clearances for the reservoir bleed need to be built into the master cylinder, which creates dead lever travel before the system pressurizes.

When the rider releases the lever, fluid pushes past the seals to refill the system which produces a non linear response in braking pressure vs rider lever pressure, the current standard for race master cylinders is for a check valve (a shim that moves to allow fluid to flow in one direction only) is added behind the main seal to speed up the fluid flow into the pressurized side of the piston when the lever is relaxed - particularly if the rider isn't fully releasing the brakes, this creates a delay in the reaction of the system to the riders input, as the pressure on the caliper side decreases below ambient, the check valve opens, fluid flows, the check valve closes again and pressure stabilizes... the rider wont realize any of this is going on, these are events happening on a very small time frame - but all add up to create that elusive "brake feel" And yes, the master cylinder is only one subsystem; within the whole, pads, lines, calipers, discs, and even tires contribute to brake feel! So what is this all about, you ask? Well, as with most engineering problems, the simplest answer is usually the best answer!

And Accossato have come up with the solution to these woes, which I am in no doubt about, and will eventually become the new standard in master cylinder technology. Why have the seals mounted to a moving (wobbly) piston? when they can be fixed into the bore of the master cylinder!? So what exactly have they done, why, and how does it work so much better than a "normal" master cylinder? As mentioned earlier—why have seals that can bend and move and change in size! and generally create lag and poor feel in the system, mounted to a piston that also moves around and has nothing keeping it in a rigidly guided, straight, and perfect path up and down the bore—

Accossato has flipped this design on its head and mounted the seals in the bore, so only the piston moves. At first glance this seems a bit "so what," but it has several key advantages. The seals still swell slightly when submerged in fluid; however, now they grow away from the bleed hole, not towards it. This means the bleed hole/piston position can be set perfectly, completely removing any free lever travel (or allowing a precise amount). Because the seals are now static in relation to the body, stiffer lip seals can be used, with a tighter-fitting piston, completely isolating the pressurized and non-pressurized sides of the piston during braking—meaning pressure is now only and instantly correlated with rider lever input. Seal wear is decreased due to less pulling and pushing of the seals. When the piston is pushing forwards and pressurizing the system, the piston is also moving in the forwards motion of the seal lip, not against it, massively reducing seal drag and improving feel. When the piston is pulling backwards, the action of the piston is working against the seal lip direction, helping to keep the system sealed until pressure is fully released from the lever, giving a linear response to the rider's reduction in lever pressure. Due to the reverse action of the piston sealing the system, it means a much faster release response, as suction literally pulls the pads back rather than relying on a passive reduction in pressure. Due to the reverse action of the piston sealing the system, it means a much faster response if brake pressure is increased again.

Technical specifications :

Machining: CNC machined
Piston diameter: 19 mm
Lever spacing: PRS 17-18-19 mm
Lever type: revolution
Bolts: galvanized steel
U-bolt: offset
Brake hose connection size: M10x1
Oil tank: not included
Stop light switch: not included

Meaning of 19 x 17 -18-19
In the description of a pump there are two values: 19 X 17-18-19. The first number indicates the diameter of the piston. The second number indicates the lever spacing.
The 19 mm diameter is ideal for dual disc systems.
The 17-18-19 mm spacing is recommended for track use, but also for road use.
To choose the best spacing, keep in mind that, for the same force exerted on the lever, the greater the spacing, the greater the force required for braking.

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