Dump valve 'adjustment' springs ?
07 September 2004, 08:09 AM
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Dump valve 'adjustment' springs ?
Can anyone explain the purpose of the adjustable springs/shims that are available for forge (and I guess others) dumpvalves.
I've just replaced the OEM plastic re-circ unit on my 98MY Turbo with a forge re-circ, primarily because the plastic one had started to weep slightly.
I 'understood' that the valve is controlled by the inlet manifold boost pipe, so cannot see the purpose of the adjustment springs ?
Also, can anyone with one of these confirm the metallic noise on valve operation (I assume that this is because it is metal, rather than plastic ?)
Cheers,
Mark
I've just replaced the OEM plastic re-circ unit on my 98MY Turbo with a forge re-circ, primarily because the plastic one had started to weep slightly.
I 'understood' that the valve is controlled by the inlet manifold boost pipe, so cannot see the purpose of the adjustment springs ?
Also, can anyone with one of these confirm the metallic noise on valve operation (I assume that this is because it is metal, rather than plastic ?)
Cheers,
Mark
07 September 2004, 11:46 AM
#2
Originally Posted by markwild
Can anyone explain the purpose of the adjustable springs/shims that are available for forge (and I guess others) dumpvalves.
I've just replaced the OEM plastic re-circ unit on my 98MY Turbo with a forge re-circ, primarily because the plastic one had started to weep slightly.
I 'understood' that the valve is controlled by the inlet manifold boost pipe, so cannot see the purpose of the adjustment springs ?
Also, can anyone with one of these confirm the metallic noise on valve operation (I assume that this is because it is metal, rather than plastic ?)
Cheers,
Mark
I've just replaced the OEM plastic re-circ unit on my 98MY Turbo with a forge re-circ, primarily because the plastic one had started to weep slightly.
I 'understood' that the valve is controlled by the inlet manifold boost pipe, so cannot see the purpose of the adjustment springs ?
Also, can anyone with one of these confirm the metallic noise on valve operation (I assume that this is because it is metal, rather than plastic ?)
Cheers,
Mark
Mark,
the shims are to increase spring load to keep closed pressure on the valve to stop fluttering on light throttle lift off , I.e pulling up to traffic lights on overrun & then it dies / wont tick over because of leakage.
As for the Metallic noise sorry cannot help , don't have a forge
Dean
07 September 2004, 12:03 PM
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Dean - thanks - I'm not entirely sure why the springs are necessary though (sorry..)
OK _ I think I need to find out how they work first
. I thought that the D/V flowed air when the pressure in the airflow side (e.g. in I/C) was greater than the pressure on the manifold side . So when the throttle is shut, the D/V releases the 'unused' pressure.
I've noticed that I get a strange effect when I partially lift, but leave positive boost on (e.g. at the end of a slip road, when joining a dual carriageway) - I guess this is because the inlet manifold pressure drops, allowing the D/V to open, but then the pressure in the i/c drops below the pressure in the manifold (which doesn't happen in a closed throttle situation), so the d/v snaps shut - so setting up a slight 'flutter'. - Is this the situation you describe ? (I've not had any tickover issues...)
If the spring is increased, does this increase the 'resistance' to open, i.e. the pressure differential required between the manifold and i/c sides of the D/V ....
Or am I talking complete twaddle ???
Mark
OK _ I think I need to find out how they work first
. I thought that the D/V flowed air when the pressure in the airflow side (e.g. in I/C) was greater than the pressure on the manifold side . So when the throttle is shut, the D/V releases the 'unused' pressure. I've noticed that I get a strange effect when I partially lift, but leave positive boost on (e.g. at the end of a slip road, when joining a dual carriageway) - I guess this is because the inlet manifold pressure drops, allowing the D/V to open, but then the pressure in the i/c drops below the pressure in the manifold (which doesn't happen in a closed throttle situation), so the d/v snaps shut - so setting up a slight 'flutter'. - Is this the situation you describe ? (I've not had any tickover issues...)
If the spring is increased, does this increase the 'resistance' to open, i.e. the pressure differential required between the manifold and i/c sides of the D/V ....
Or am I talking complete twaddle ???
Mark
07 September 2004, 02:23 PM
#4
Originally Posted by markwild
Dean - thanks - I'm not entirely sure why the springs are necessary though (sorry..)
OK _ I think I need to find out how they work first . I thought that the D/V flowed air when the pressure in the airflow side (e.g. in I/C) was greater than the pressure on the manifold side . So when the throttle is shut, the D/V releases the 'unused' pressure.
I've noticed that I get a strange effect when I partially lift, but leave positive boost on (e.g. at the end of a slip road, when joining a dual carriageway) - I guess this is because the inlet manifold pressure drops, allowing the D/V to open, but then the pressure in the i/c drops below the pressure in the manifold (which doesn't happen in a closed throttle situation), so the d/v snaps shut - so setting up a slight 'flutter'. - Is this the situation you describe ? (I've not had any tickover issues...)
If the spring is increased, does this increase the 'resistance' to open, i.e. the pressure differential required between the manifold and i/c sides of the D/V ....
Or am I talking complete twaddle ???
Mark
OK _ I think I need to find out how they work first
. I thought that the D/V flowed air when the pressure in the airflow side (e.g. in I/C) was greater than the pressure on the manifold side . So when the throttle is shut, the D/V releases the 'unused' pressure. I've noticed that I get a strange effect when I partially lift, but leave positive boost on (e.g. at the end of a slip road, when joining a dual carriageway) - I guess this is because the inlet manifold pressure drops, allowing the D/V to open, but then the pressure in the i/c drops below the pressure in the manifold (which doesn't happen in a closed throttle situation), so the d/v snaps shut - so setting up a slight 'flutter'. - Is this the situation you describe ? (I've not had any tickover issues...)
If the spring is increased, does this increase the 'resistance' to open, i.e. the pressure differential required between the manifold and i/c sides of the D/V ....
Or am I talking complete twaddle ???
Mark
Dean
08 September 2004, 08:08 AM
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Thanks Steve
t.b.h. I'm going to do some tests with the 2 valves, as the oem one does seem to handle the job better - I just need to prove its not leaking .
t.b.h. I'm going to do some tests with the 2 valves, as the oem one does seem to handle the job better - I just need to prove its not leaking .
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