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What is a Blow-Off valve? What does it do?

What is the application of Blow-off valves

There are many different types and models of blow-off valves, but they all serve the same purpose - they release the pressure generated by the turbocharger into the atmosphere when the throttle is closed.

What is the purpose of a blow off valve?

Jak działa zawór blow off firmy Properfekt?


The Blow-off valve is actually a bleed valve that releases turbo / boost pressure when the throttle is closed. While the turbo is still spinning and generating pressure. The pressure wave, when the throttle is closed , returns to the turbocharger. This causes the compressor wheel to slow down very quickly. This is detrimental to the rotor bearing and reduces the life of the turbo. In addition, with the next opening of the throttle, it delays the recovery of the full turbo boost and thus the turbocharger will not be able to deliver the maximum boost as quickly as desired.

What is a dump valve and how does it work?

There are two different bleed valves; recirculation (DV - diverter valve type) and atmospheric bleed valves (blow off / BOV type). A recirculating valve is one in which boost pressure is recirculated back into the intake, in such a way that it does not affect the fuel-air mixture already measured by the flow meter.

An atmospheric blow-off valve is one in which air is released into the atmosphere instead of being reused.

How does the Blow off valve work?


Jak działa zawór blow off firmy Properfekt? At engine idle:

Engine vacuum at the top of the BOV tries to force the piston open. There is no vacuum or pressure at the bottom of the piston. The vented BOV must remain closed at idle to avoid leaks. To make this possible, there is a stainless steel spring inside the top housing of the BOV that keeps the piston closed.
Properfekt offers two-piston models on most of its valves. One piston - the main one is aluminum, and the auxiliary one is Teflon, which is just responsible for sealing the valve at idle.


At low boost:

The conditions experienced by the blow off at low boost are similar to when the car is idling, but there is less vacuum present at the top of the piston, this is because the throttle is slightly more open. If the correct spring is fitted to keep the piston closed at idle, the piston will also be closed at low boost. Our products come with two main springs, with which you will tune the valve's operating characteristics at both low boost and high boost.


At high boost:

At high boost, the valve is fully closed due to boost pressure at the top of the piston. When the throttle closes at high boost, the pressure at the top of the piston will turn into vacuum, the pressure in the intake system and the vacuum at the top of the piston will force the main piston as well as the auxiliary piston to rise to the top housing, causing the boost pressure to be dissipated to atmosphere. This effectively prevents the turbocharger from being slowed down by excess boost pressure. This is when the familiar and distinctive sound of bleeding air occurs.


Where should the blow off valve be installed?

Blow off is a separate part that should be mounted on the hose or intake pipe between the turbocharger compressor and the throttle valve. Mounting directly in the intercooler side tank is also acceptable.


What are the ways to install blow-off valves?

Jak działa zawór blow off firmy Properfekt?

The most common way to install a blow-off valve is with a spigot and a straight or angled silicone connector. In this case, the intake pipe must have a spigot of the same diameter (possibly boil silicone reduction).

Another way is rigid mounting with a V-Band type connector. We use this type of connection in our most powerful models.


What should be the vacuum source for the blow off valve?

To ensure proper operation of the valve, the best possible vacuum source must be provided. It must come from behind the throttle, preferably from the intake manifold. The diameter of the source port must be equal to or larger than the port on the valve. Avoid sharing the vacuum hose via tees with other accessories such as vacuum timers.


What is the difference between Properfekt Blow-off valves and the cheap copy from China?

Jak działa zawór blow off firmy Properfekt?

The more expensive blow off valves outperform the copies with quality workmanship and more precise fits along with far more durable sealing components. All this is to make the blow off valve more accurate, responsive and capable of higher boosts and horsepower.

It is very common for Chinese blow off valves to malfunction or not work at all at higher boost pressures. This is usually due to leakage, insufficient vacuum or internal resistance to piston movement.

We have put a lot of effort into engineering our bleeder valves. We make every effort to maintain the same high standard when manufacturing all of our products.
Our products are based on work entirely made in the European Union from the finest materials available.

You can check our Blow off valves products here.

Jak działa zawór blow off firmy Properfekt?