Valve Bleed Flow

ReStackor Demo

Buy Now

"Clicker" flow rates are accurately computed in ReStackor pro calculations

Calculation of orifice bleed circuit "clicker" flow is a fundamental capability in ReStackor used to relate changes in the stack stiffness to the fluid flow rate through the bleed clickers. With accurate bleed circuit calculations you can use ReStackor to tune the stack to be 2 clicks softer at low speed to deal with chop and 3 clicks stiffer at mid speed to handle whoops. ReStackor calculations use well founded industrial standard relationships for calculation of the bleed circuit flow rates.

Accurate calculation of flow rates through orifices has a huge industrial importance for everything from petroleum refineries to production of pharmaceuticals. Due to this industrial importance huge development efforts have been spent to arrive at a set of equations capable of accurately computing flow rates through orifice metering circuits. These relationships account for effects of flow geometry, orifice length, flow velocity as well as fluid viscosity.

ReStackor pro uses basic geometry relationships to determine the bleed circuit flow area

Flow area through the bleed port is determined using the clicker settings and a simple cone shape for the needle geometry.

Flow area through the bleed circuit clickers determined from the system geometry

Three effects control flow losses through the bleed circuit: entrance losses; expansion losses; and skin friction losses over the port length. Bleed ports are typically quite long as the port extends all the way through valve and hub of the shim stack. At high suspension speed the long port will generate appreciable skin friction losses. This causes the effect of bleed to naturally reduce at high suspension speeds. This high speed behavior is different from other bleed mechanisms, such as stack float, which persist over the entire range of suspension speeds.

Supercross-Online data

The www.supercross-online.de data for flow rate and pressure drop through an orifice is shown below.

Bleed circuit orifice flow data from supercross-online.de

This is real world data and is subject to all of the problems of real world experiments. The bleed circuit data shows a pressure drop of zero at an orifice flow rate of 4 L/min. There is a leak. The 4 L/min leak was subtracted from the flow rate and the corrected “leak free” 10wt orifice data is plotted below for use in comparison with ReStackor calculation results.

Can pressure drops through suspension flow circuits be accurately computed?

ReStackor calculations match the supercross-online orifice flow data. The 30 L/min flow rate used in these tests is equivalent to wheel speeds of 600 in/sec in an actual suspension system. The test data spans the range of low speed to high speed suspension operation and demonstrates that ReStackor calculations are capable of accurately modeling the entire range of suspension speeds.

ReStackor pro calculations for bleed circuit flow rates accurately match dyno data.

ReStackor uses well known, well anchored, industry standard fluid dynamic models to compute flow losses through the suspension valve circuits. The capability of ReStackor to accurately compute flow losses through the bleed circuits is a critical capability allowing you to experiment with different clicker settings to find suspension damping rates that work in different situations such as whoops and rocks. The tuning process then becomes one of simply modifying the shim stack stiffness to reproduce the flow area needed to match proven clicker settings at different wheel velocities.