L

Lapsley

Member
The PAP page G4-1 requires that you add one gallon of fuel after flushing all fuel out and then pump this one gallon out in under 180 seconds (20 gal/hr).

I cannot come any where near this. Topically over 10 minutes. The last few oz takes forever.

I have removed the tank and opened the access cover. With a dental pick I have verified that the weep holes between the sump chamber and the aft chamber are open and clear of sealant. Also I have verified that the flow from the reservoir (Fwd right)chamber is OK.

The problem appears to be that the flow rate from the aft chamber to the sump chamber is inadequate to support the 180 sec time period. At this fuel level (head) it supports about a 6 gal/hour flow rate.

Of course the higher the flow rate between the aft chamber and the sump chamber the higher the flow backwards when climbing (bad).

Any suggestions.
 
As I recall, I was at about 100 seconds.

Have you eliminated the other variables? Plumbing, obstructions, etc. Have you checked the gascolator screen? Add enough fuel to the tank to ensure the level is over the baffle and re-check. If you then get a good time, the holes at the bottom of the baffle might be clogged with debris or clogged with tank sealant. The test also ensures the rest of the plumbing is OK.
 
Last edited:
Same problem, but

I noticed that I had almost a full stream of fuel for the first several seconds and after that the pump got noisy and the fuel flow dropped off dramatically. It appeared that the pump wasn;t picking up fuel and was cavitating-- fuel coming out of hose was nowhere near a full stream. I put in two gallons and pumped out a gallon in less than the required time. Apparently my fuel pickup isn't quite at the bottom, so I've got maybe a half-gallon of "unsable fuel". Add some more fuel before you tear the system apart more.

Wayne 120241/N143WM flying
 
finger screen

Another thing to check is the screen at the tank outlet. If little pieces of tank sealant have collected around the base of the screen, there will be reduced flow when the tank is almost empty.
Joe
 
PAp Fuel Flow

Fuel flow continued

I have removed the tank and leveled it on my bench. I have removed the access cover.

The PAP procedure for the height of the sump drain fitting bt first putting 1 gal in and pumping it out. Since I have the access cover off I can see the sump and verify that when drained to the unusable level that the sump is almost empty, so the screen is not clogged. A dental pick inserted in the weep holes between the aft chamber and the sump chamber shows no indication of proseal in the weep holes.

I have measured the flow rate for various fuel levels and it measures under 20 gal/hour until about 5 Gal.\

If I can figure out how to post a chart I will.

Roger
 
Tiny inlets

Hi Lapsley,
Did you manage to sort out the cause of the low test flow rate? Today I did my test and the flow rate didn't meet the standard. I have some ideas about how to investigate further, but I would really appreciate your opinion

When I built the tank, I worried about those tiny inlets to the tank centre section. So I pulled strips of cloth through them to be sure no proseal was hiding. The purpose of the inlets was obvious enough, but the assembly method ruled out any way to check the sectional area of the inlets. I found that quite odd and out of character with the test of the design. It seemed that the flanges would only need to be bent 1/32 inch out and the hole cross sections would change dramatically.
Despite my reservations , I rechecked them again and put the lid on.
Rod
 
Rod & Roger,

FYI: I too had a low flow rate that just exceed minimum time in the PAP but the pressure was nothing... it never got higher than 1 psi (with the engine not running).

Anyway, the pump completely failed last Saturday with only 13.1 hr. on the engine. I ordered two, installed one and I also installed an OTTO switch.

-Ron
 
Otto?????

Who's this guy Otto? Just kidding, I Googled it. Been hearing several comments about this option that is apparently incorporated in the circuit board, but not used. Is there a place on the board for this switch to mount? How much trouble to install it? Sounds like a nice upgrade after certification. Really don't need that pump running all the time using power and wearing itself out. We PA-28 drivers are used to using the aux pump for T/O and landing only.
 
PAP Data Continued.

To solve this problem I opened up the rwo weep holes between the aft chamber and the sump chamber. I did this slowly using first a single $# 40 drill. I ended up with two #30 holes in the inboard weep hole and 2 # 40 weep hole in the outboard weep holes. Now my flow meets the PAP requirement of 20 gal per hour with one gal of fuel. It also provides adequate fuel flow for operation for the 1 gal unusable. I can only assume that even though I took care when building the tank to keep the weep holes clean that I must have allow some proseal to block the weep holes.


Roger
 
You must log in or register to reply here.