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<blockquote data-quote="Black306" data-source="post: 7581013" data-attributes="member: 4780"><p>Yea, I've done a bit of testing and found that the PPRV function may be a bit more complicated than the public believes. I thought that the PPRV was simply a couple valves consisting of a check valve and a blow off valve. I'll try to illustrate with the following pictures.</p><p></p><p><img src="http://westcoastmustangs.com/temp/pprv_flow1.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>What I believed is that the PPRV had 2 simple functions: (1) with the use of a check valve, maintain fuel pressure for quicker restarts, and (2) with the use of a blow off valve, bleed off <em>any</em> excessive fuel pressure. Using the picture above, the check valve allows for flow in the red arrow direction, the blow off valve allows flow in the blue arrow direction, and the green arrow represents a chamber in the PPRV which allows excessive pressure to move to the blow off valve (I'll call this the output chamber). However, I find the PPRV is not as simple as that.</p><p></p><p><img src="http://westcoastmustangs.com/temp/pprv_flow2.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>If you notice in the above pic, the lower green arrow represents a second chamber where fuel is allowed to flow from the PPRV's inlet right to the small nipple on the left (I'll call this the input chamber). Think about that for just a second. Fuel, coming from the pumps, is allowed to enter the PPRV, head towards the small nipple via the input chamber, and exit that small nipple. The only regulatory device is the fact the small nipple actually has a very small hole. Now, that function kinda baffles me. Why would the engineers design a part that is basically a controlled leak (based only by the hole's size) for the fuel system? At all times, a small amount of fuel is allowed to come out of that nipple regardless of engine operation.</p><p></p><p>Let me run this scenario. Car is at WOT, rail pressure is 39psi + actual boost. That means pressure in both chambers is roughly rail pressure with the nipple blowing off some fuel. Now, foot is off the gas, injectors close, pumps run for a short period of time longer, and fuel pressure spikes. What I though occurred was that the blow off valve of the PPRV expelled the excessive pressure out the small nipple (as represented in the 1st picture) even though the pumps were still pumping after the injectors closed. However, I don't think that's the case. With the PPRV as described in the 2nd picture, rail pressure will only <em>begin</em> to come down when the pumps are slowed down or shut off. This would occur because the pumps are not pumping fuel into the PPRV, and therefore the blow off valve would expel excessive pressure into the input chamber (as represented by the lower green arrow) when pressure in the input chamber is lower than the output chamber. Excessive pressure is not simply expelled out the small nipple when pressure exceeds 67psi. (I hope this makes sense.)</p><p></p><p>Let me put it in other words........as designed, the PPRV only reduces rail pressure <em>after</em> the pumps are commanded to reduce pressure. The PPRV does nothing to protect against pressure spikes to begin with. This means, if the pumps were allowed to continue much after the injectors are shut off, pressure would spike beyond the ~67psi blow off amount.</p><p></p><p>I'm still waiting for another PPRV I bought from another member to make sure this is the case. I didn't confirm the operation of the PPRV before trying to modify it. If what I think is true, the size of the hole in the nipple plays a significant role of the whole function of the PPRV. A modified PPRV may entail more than just removing the check valve. It would also include blocking the path of fuel from the input opening to the small nipple (basically, sealing the input chamber). </p><p></p><p>I really wish I could pick the brains of the engineer(s) that designed this part.</p></blockquote><p></p>
[QUOTE="Black306, post: 7581013, member: 4780"] Yea, I've done a bit of testing and found that the PPRV function may be a bit more complicated than the public believes. I thought that the PPRV was simply a couple valves consisting of a check valve and a blow off valve. I'll try to illustrate with the following pictures. [img]http://westcoastmustangs.com/temp/pprv_flow1.jpg[/img] What I believed is that the PPRV had 2 simple functions: (1) with the use of a check valve, maintain fuel pressure for quicker restarts, and (2) with the use of a blow off valve, bleed off [i]any[/i] excessive fuel pressure. Using the picture above, the check valve allows for flow in the red arrow direction, the blow off valve allows flow in the blue arrow direction, and the green arrow represents a chamber in the PPRV which allows excessive pressure to move to the blow off valve (I'll call this the output chamber). However, I find the PPRV is not as simple as that. [img]http://westcoastmustangs.com/temp/pprv_flow2.jpg[/img] If you notice in the above pic, the lower green arrow represents a second chamber where fuel is allowed to flow from the PPRV's inlet right to the small nipple on the left (I'll call this the input chamber). Think about that for just a second. Fuel, coming from the pumps, is allowed to enter the PPRV, head towards the small nipple via the input chamber, and exit that small nipple. The only regulatory device is the fact the small nipple actually has a very small hole. Now, that function kinda baffles me. Why would the engineers design a part that is basically a controlled leak (based only by the hole's size) for the fuel system? At all times, a small amount of fuel is allowed to come out of that nipple regardless of engine operation. Let me run this scenario. Car is at WOT, rail pressure is 39psi + actual boost. That means pressure in both chambers is roughly rail pressure with the nipple blowing off some fuel. Now, foot is off the gas, injectors close, pumps run for a short period of time longer, and fuel pressure spikes. What I though occurred was that the blow off valve of the PPRV expelled the excessive pressure out the small nipple (as represented in the 1st picture) even though the pumps were still pumping after the injectors closed. However, I don't think that's the case. With the PPRV as described in the 2nd picture, rail pressure will only [i]begin[/i] to come down when the pumps are slowed down or shut off. This would occur because the pumps are not pumping fuel into the PPRV, and therefore the blow off valve would expel excessive pressure into the input chamber (as represented by the lower green arrow) when pressure in the input chamber is lower than the output chamber. Excessive pressure is not simply expelled out the small nipple when pressure exceeds 67psi. (I hope this makes sense.) Let me put it in other words........as designed, the PPRV only reduces rail pressure [i]after[/i] the pumps are commanded to reduce pressure. The PPRV does nothing to protect against pressure spikes to begin with. This means, if the pumps were allowed to continue much after the injectors are shut off, pressure would spike beyond the ~67psi blow off amount. I'm still waiting for another PPRV I bought from another member to make sure this is the case. I didn't confirm the operation of the PPRV before trying to modify it. If what I think is true, the size of the hole in the nipple plays a significant role of the whole function of the PPRV. A modified PPRV may entail more than just removing the check valve. It would also include blocking the path of fuel from the input opening to the small nipple (basically, sealing the input chamber). I really wish I could pick the brains of the engineer(s) that designed this part. [/QUOTE]
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