Dump valve question
Discussion
Firstly who has a dump valve?
I was just wondering if on idle your dump valve is open? I know that on idle they are ment to be open. But for some reason mine is not??
It works fine and im not getting any pressure loss, but it is very much closed on idle?
It is a bailey single piston.
I was just wondering if on idle your dump valve is open? I know that on idle they are ment to be open. But for some reason mine is not??
It works fine and im not getting any pressure loss, but it is very much closed on idle?
It is a bailey single piston.
I have a BOV (Baily I think) on my S4s and no it shouldn't be open on Idle as there isn't enough vaccum.
The Blow Off Valve/Dump Valve that is fitted to many turbo cars works by relieving vaccum pressure in the inlet system that would normally put unneeded pressure on the turbo blades and bearings. They are normally set to 1bar or above so that they would normally only work under initial deceleration from a high rev/boost condition.
(please someone correct me if that is near enough)
Under idle your car would only be producing a small amount of vaccum to draw air/fuel into the system.
Del
S4s
>> Edited by Del-Esprit on Sunday 15th February 13:51
The Blow Off Valve/Dump Valve that is fitted to many turbo cars works by relieving vaccum pressure in the inlet system that would normally put unneeded pressure on the turbo blades and bearings. They are normally set to 1bar or above so that they would normally only work under initial deceleration from a high rev/boost condition.
(please someone correct me if that is near enough)
Under idle your car would only be producing a small amount of vaccum to draw air/fuel into the system.
Del
S4s
>> Edited by Del-Esprit on Sunday 15th February 13:51
Kev, I know what your problem is or at least I think I do. You need a twin piston type not a single piston. This is because you have an air flow meter and ECU. I know single piston DV cause all sorts of problems at idle if you have an air flow meter. Ring me on 0771 775 0453 and I should be able to help.
Cheers,
Dave Walters
Cheers,
Dave Walters
Firstly,my knowledge on this is very little.
I always thought Blow off valves and Dump valves to be one and the same until 'Lotusguy'(Jim) posted a very imformative reply here (april 25th) last year.
Do a search for 'bov dump valves' on this forum,i found it interesting enough to remember anyway
PAUL C
I always thought Blow off valves and Dump valves to be one and the same until 'Lotusguy'(Jim) posted a very imformative reply here (april 25th) last year.
Do a search for 'bov dump valves' on this forum,i found it interesting enough to remember anyway
PAUL C
Some of the difference is also just names people call things. Dump Valve is a common name in the UK/Europe but Blow Off Valve in the US. They are referring to the identical item with same process but it may be slightly technically incorrect depending upon which technical book you happen to read.
A dump valve as mention in the article that vents pressure rather than vaccum is also known as a pop off ,poppit or relief valve in the UK, I believe.
Whatever the name we all know what is meant but always worth double checking if in doubt.
This is just my appreciation of this difference.
A dump valve as mention in the article that vents pressure rather than vaccum is also known as a pop off ,poppit or relief valve in the UK, I believe.
Whatever the name we all know what is meant but always worth double checking if in doubt.
This is just my appreciation of this difference.
Hi,
Paul C. Thanks for the mention. Seems this issue is constantly resurfacing, so with permission of the author (me), I will reprint the explanation of the two very disimilar devices which are often confused.
Seems a little further clarification is in order. A Blow-Off Valve (BOV) and a Dump Valve (used on Lotus Carb Turbos) are different animals.
A Dump Valve is a basic pressure relief Valve and is sometimes called a Pop-Off Valve. Have you ever seen or used a household pressure cooker. That little device on top of the lid that vents steam pressure to keep the pot roast from being Blown all over the ceiling is, in essence, a Dump Valve.
A boost Dump Valve monitors the pressure within the plenum upstream from the throttle plates and vents when the boost pressure reaches a pre-set limit.
It is not a smart Valve, it's oblivious to throttle position, intake manifold pressure/vacuum or turbo rpm. The Dump Valve "single mindedly" monitors plenum pressure and vents excess pressure without consideration for other factors. When the plenum pressure drops below the preset limit, the Valve closes again.
The Dump Valve will vent during full throttle conditions anytime the boost pressure exceeds the preset limit for whatever reason. It will also vent
when the throttle is closed abruptly during a boost condition. When the throttle closes the turbo output suddenly has no where to go, and the plenum pressure spikes. The Dump Valve will open if/when the spike exceeds the preset limit, govern by the spring in the Valve, and close again when the pressure drops and is overcome by the spring pressure again.
The Dump Valve opens a large orifice sized to quicly vent excess pressure. But when it closes again, the turbo is still spinning and quickly pressurizes the plenum back above the preset limit, so the Dump Valve opens again at least partially. The cycle repeats until the turbo slows to the point at which it can no longer pressurize the plenum beyond the limit. The cycle occurs rapidly and seems more like a "flutter". The fluttering vent cycle is what produces the characteristic "Horse Whinney".
A Blow Off Valve is similar to a Dump Valve, but adds an external control circuit and vents the plenum in response to throttle position. A Throttle Position Switch (TPS) could be used to actuate the BOV, but on older carburetted non-ECU engines, as well as aftermarket additions, the BOV typically monitors manifold vacuum downstream from the throttle plates since closed throttle = high manifold
vacuum. A vacuum port is located in the side of the intake manifold where it will be 1) immediately downstream from the throttle plates when they are
fully closed and 2) upstream from the plates as soon as they are cracked open. A vacuum line runs from that port to a diaphragm in the BOV.
When the throttle is closed, the port applies high vacuum to the BOV diaphragm to open the Valve and vent plenum pressure. When the throttle is cracked open, the throttle exposes the port to plenum pressure, killing the vacuum at the diaphragm and closing the Valve. Hence, the BOV operates in response to throttle position, venting the plenum when the throttle is closed. It remains open/ venting as long as the throttle remains closed. Typically the BOV does not cycle or flutter, so the usual sound is one smooth whistle... no flutter.
If the throttle is slammed shut when the turbo is fully spooled up and at full boost, the sudden high back pressure condition can physically damage
the compressor wheel, and will definitely cause the turbo to rapidly slow down. Then when the throttle is opened again, the turbo will have to accelerate again before achieving full boost. The result is "turbo lag".
The BOV vents the plenum back pressure, allowing the turbo to keep spinning at high rpm, and preventing the damaging pressure surge.
The Dump Valve is a pressure relief / over-boost protection device, whereas the BOV is a throttle-sensitive plenum vent.
The waste gate is quite different in that it does not vent plenum pressure. It vents exhaust gasses, by-passing the turbine wheel in order to control
the amount of boost produced in the first place. Dump and Blow-Off Valves limit boost "after" it's delivered to the plenum.
The wastegate and Dump Valve both monitor "plenum pressure" and act to control and limit available boost levels. The Blow-Off Valve monitors "throttle position" (manifold pressure) and vents the plenum to kill any boost present at times when boost is not wanted (closed throttle). Hope this better explains the two. Happy Motoring!...Jim '85TE
Paul C. Thanks for the mention. Seems this issue is constantly resurfacing, so with permission of the author (me), I will reprint the explanation of the two very disimilar devices which are often confused.
Seems a little further clarification is in order. A Blow-Off Valve (BOV) and a Dump Valve (used on Lotus Carb Turbos) are different animals.
A Dump Valve is a basic pressure relief Valve and is sometimes called a Pop-Off Valve. Have you ever seen or used a household pressure cooker. That little device on top of the lid that vents steam pressure to keep the pot roast from being Blown all over the ceiling is, in essence, a Dump Valve.
A boost Dump Valve monitors the pressure within the plenum upstream from the throttle plates and vents when the boost pressure reaches a pre-set limit.
It is not a smart Valve, it's oblivious to throttle position, intake manifold pressure/vacuum or turbo rpm. The Dump Valve "single mindedly" monitors plenum pressure and vents excess pressure without consideration for other factors. When the plenum pressure drops below the preset limit, the Valve closes again.
The Dump Valve will vent during full throttle conditions anytime the boost pressure exceeds the preset limit for whatever reason. It will also vent
when the throttle is closed abruptly during a boost condition. When the throttle closes the turbo output suddenly has no where to go, and the plenum pressure spikes. The Dump Valve will open if/when the spike exceeds the preset limit, govern by the spring in the Valve, and close again when the pressure drops and is overcome by the spring pressure again.
The Dump Valve opens a large orifice sized to quicly vent excess pressure. But when it closes again, the turbo is still spinning and quickly pressurizes the plenum back above the preset limit, so the Dump Valve opens again at least partially. The cycle repeats until the turbo slows to the point at which it can no longer pressurize the plenum beyond the limit. The cycle occurs rapidly and seems more like a "flutter". The fluttering vent cycle is what produces the characteristic "Horse Whinney".
A Blow Off Valve is similar to a Dump Valve, but adds an external control circuit and vents the plenum in response to throttle position. A Throttle Position Switch (TPS) could be used to actuate the BOV, but on older carburetted non-ECU engines, as well as aftermarket additions, the BOV typically monitors manifold vacuum downstream from the throttle plates since closed throttle = high manifold
vacuum. A vacuum port is located in the side of the intake manifold where it will be 1) immediately downstream from the throttle plates when they are
fully closed and 2) upstream from the plates as soon as they are cracked open. A vacuum line runs from that port to a diaphragm in the BOV.
When the throttle is closed, the port applies high vacuum to the BOV diaphragm to open the Valve and vent plenum pressure. When the throttle is cracked open, the throttle exposes the port to plenum pressure, killing the vacuum at the diaphragm and closing the Valve. Hence, the BOV operates in response to throttle position, venting the plenum when the throttle is closed. It remains open/ venting as long as the throttle remains closed. Typically the BOV does not cycle or flutter, so the usual sound is one smooth whistle... no flutter.
If the throttle is slammed shut when the turbo is fully spooled up and at full boost, the sudden high back pressure condition can physically damage
the compressor wheel, and will definitely cause the turbo to rapidly slow down. Then when the throttle is opened again, the turbo will have to accelerate again before achieving full boost. The result is "turbo lag".
The BOV vents the plenum back pressure, allowing the turbo to keep spinning at high rpm, and preventing the damaging pressure surge.
The Dump Valve is a pressure relief / over-boost protection device, whereas the BOV is a throttle-sensitive plenum vent.
The waste gate is quite different in that it does not vent plenum pressure. It vents exhaust gasses, by-passing the turbine wheel in order to control
the amount of boost produced in the first place. Dump and Blow-Off Valves limit boost "after" it's delivered to the plenum.
The wastegate and Dump Valve both monitor "plenum pressure" and act to control and limit available boost levels. The Blow-Off Valve monitors "throttle position" (manifold pressure) and vents the plenum to kill any boost present at times when boost is not wanted (closed throttle). Hope this better explains the two. Happy Motoring!...Jim '85TE
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