Rail and pressure relief valve one E-BAY

[COSEng]

Wasn't someone looking for a pressure reilef valve to

play with???



http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7956046056&category=33553

 

[Matt400]

In looking at the set up in the pic and on my truck along with being fairly new to Diesels my thinking may be too simplistic but lets consider that:

• The limit valve is the main concern for pressure boxes
  
• Each time pressure opens it it weakens
  
• They cost $455. 00
  
• You can't buy one without giving up a VIN#
  

Now consider that:

• Bosh claims 30,000 psi is ok for the pump
  
• Pressure boxes won't even go that high
  
• The limit valve only opens on over pressure
  

So... what would be wrong with removing the the limit valve and the short piece of fuel pipe and put a plug in both ends where it once connected, put it away for safe keeping and run a pressure box of choice?



Is this too simple or are there other reasons its there such as a "surge" suppressor that keeps the rail from cracking or other hydraulic damaging vibrations and the limit valve is actually functioning/opening more than we know. If it stays seated all the time and no fuel runs through that pipe I say take it off... am I nuts!? :-laf

 

[JHardwick]

your nuts, but that's beside the point

 

[JHardwick]

BTW, I think your logic is acceptable, but the 30,000 is a little off tempo :-{}

 

[rbattelle]

So... what would be wrong with removing the the limit valve and the short piece of fuel pipe and put a plug in both ends where it once connected, put it away for safe keeping and run a pressure box of choice?

I agree with Jeff... you're nuts! :-laf But they told Edison the same thing about the light bulb!



Seriously, I understand what you're getting at, but I see 2 problems. First is safety. You've got to have a safety in a system capable of 1600 bar. There's just no getting around that.



Second, I think (someone correct me if I'm wrong) that the problem with very high fuel pressures is the rail pressure sensor reading excessive pressure and setting a code in the ECM rather than problems with the limiting valve opening.



-Ryan

 

[rbattelle]

How much is that whole assembly at the dealer?



-Ryan

 

[Matt400]

How much is that whole assembly at the dealer?



-Ryan

Hey Ryan, I checked its 455. 00 and comes just like the one on eBay.



rbattelle,

I bet the pressure sensor would tip off the ECM to do a check engine lamp before that valve opens so using that as a warning to back down the pressure should be good enough.



JHardwick,

I proly am nuts The 30,000 number I got is second hand info from TS Performance who confirmed with Bosh the HPCR system is good to run all day long under that number.

 

[rbattelle]

$455 isn't that bad for that assembly. I considered bidding on the one on Ebay (final price was $100). $100 for a "toy" to do experiments on is too steep, and I'd be concerned about using it as a spare part since its real history is unknown...



-Ryan

 

[Matt400]

$100 for a "toy" to do experiments on is too steep

True and I don't think there is much to experiment with anyway.

The limit valve appears to be a sealed unit so you cant just take it apart and change to a more heavy spring plus if you were doing that it wouldn't make much sense when current pressure boxes won't exceed the systems safe operating range anyway.

 

[rbattelle]

Well, really I just wanted to experiment with the pressure sensor.



-Ryan

 

[Matt400]

I see.

I wouldn't mind finding out how the outlook monitor is able to convert data from that sensor into a rail pressure reading you can monitor. A SPA digital gauge would be nice- that way I could program a warning lamp set point and also program an even higher set point to trigger emergency shut down. Then I would pull that silly limit valve off for sure.



Its probably only a matter of time till one of the bigger vendors build a replacement valve with a little higher pop off pressure.



After studying the circuit further I see that the real trouble with removing that valve would be a worse case scenario where the (FCA) Fuel Control Actuator were to malfunction or stick in the open position. If that were to happen then uncontrolled fuel pressure would result. and most likely is the reason Cummins put it there. Might never happen but an engineer proly said. . "what if?"

 

[rbattelle]

Matt,



With the help of DLeno (who pointed out the proper circuit to me) I figured out how to build a fuel rail pressure gauge. Read about it in this thread. I have not yet built one, because I used to be wary about splicing into the stock transducer. I'm no longer wary about it, and I intend to do this as an add-on to my big fuel system project (here).



-Ryan

 

[JHardwick]

JHardwick,

I proly am nuts The 30,000 number I got is second hand info from TS Performance who confirmed with Bosh the HPCR system is good to run all day long under that number.

TDR issue 47 page 59 says the pressure limiting set point is ~28,000lbs, but the test truck blew off at 26,000lbs. This sounds more like what I've been reading over the last couple of years.



The test truck blowing off 2,000lbs shy of the set point could be a weakening of the valve, which is also kinda what I've read. The vavle is supposed to be a safety valve, not a fueling valve like you'd see on a constant flow injection set-up.

 

[Matt400]

I know. . I read that too and always thought 28K was the limit. Even Banks limits the 6 gun with speedloader to 27K. But we are talking about two different things. .

TS confirmed with Bosh the "pump" is good all day long at 30K, no mention was made about the limit valve.



TS's theory why the limit valve won't open with their box is due to the variable and increasing pressure at various throttle settings it makes vs a bunch of pressure setting dead headed on the rail you would see from a competitors box.



I am sure the limit valve is just a heavy spring so to me pressure is pressure no matter how much volume is flowing on the other side so I don't completely understand why it would open at 29K at part throttle but not at full throttle yet thats what TS says.

Maybe I misunderstood TS and they are "commanding" 29K at WOT but "actual" pressure on the rail is less due to the large volume of fuel the injectors are passing, now that would make more sense and is another great reason for gauges with making mods.

 

[Matt400]

Ryan,

I read through the thread on your fuel system. . whew! fun stuff.

I really like the idea of PWM on the FP, it would make it last longer I bet.

Speaking of the FP, I wasn't sure how you are going to supply power. One of your circuits includes the ECM but yet you have that toggle??



If you are not doing it already consider using the OE FP circuit so that in case of an accident and you were unconscious with the key on- the ECM will shut down the FP, wouldn't want #2 spraying all over should a line be severed.



Super big thanks for pointing out dan. poitras post on the OE pressure sensor calcs.

Using those calcs and the unique programing features of the SPA pressure gauge it is possible to monitor both high pressure and low pressure on a single digital dual gauge.

On your system if you monitor low pressure you will be able to "dial back" the PWM to just what the injection pump needs and not over or under power it.



If you still need a connector for the fuel pressure sensor and your gauge check with TS Performance because their Ramifier splices into that sensor, they may sell you just a harness. Now I may have to get to work on a dual high/low pressure gauge.

 

[rbattelle]

Ryan,

I read through the thread on your fuel system. . whew! fun stuff.

I really like the idea of PWM on the FP, it would make it last longer I bet.

Speaking of the FP, I wasn't sure how you are going to supply power. One of your circuits includes the ECM but yet you have that toggle??



If you are not doing it already consider using the OE FP circuit so that in case of an accident and you were unconscious with the key on- the ECM will shut down the FP, wouldn't want #2 spraying all over should a line be severed.

My diagram must be unclear. I am using the ECM LP signal to trigger the LP, but included in the circuit is a manual switch that allows me to engage the lift pump on my own for things like fuel transfers, refilling after a filter change, etc. I used a bridged double relay to achieve this, so that there is absolutely no feedback from my manual switch to the ECM (in order to prevent frying the ECM). In normal use, the ECM has full control over the LP. The power source for the LP, however, will come from one of the continuous lines on my auxillary fuseblock, then through the PWM (assuming it works as advertised).



-Ryan