Andair fuel pump blows fuse. RV-9A

[ron sterba]

Went to do my first taxi test. (XIO-320 Lycoming). Andair boost pump came to life,first by fast clicking sound for 3-4 seconds then slow clicking for 2 seconds and the 5 amp fuse blew. 5 amp is what instructions called for. New fuse put in, this time disconnected hot lead to pump relay, loaded, wiggled wires,switch on and off. Hooked hot lead to relay, same sequence of noises then 5 amp fuse blew. I so I thought that the relay function to stop pumping after back pressure build up might be the problem. So figuring i hear the the pump ramp up fast clicks that I would turn off the switch to the Andair boost pump. I used this technique 3 times. Turned the starter on and the new lycoming engine and came to life. A lot quieter because of the Vetterman mufflers. ( iam not a Harley guy). I put only 2.5 US gallons of 100LL in each tank. Ok idle adjusted to 800 rpms +|_ 35 rpms as shown on the Dynon display. Shut it down after 4 minutes. Switched tank selector to see if I could (left tank) fuel pumped through empty line on left tank. Did same sequence of just 3 seconds bursts of boost pump switch for 4 times. Tried start up after 5 seconds the engine started, never missed a beat for 4 minutes of taxi time no leaks.

I emailed Mr PHILLIPS at Andair over the weekend so some time this week I expect to hear. Didn't notice any problem around Andair pump. I didn't see and expected noises from reading instructions other than expecting a pump to make noise if it runs. I just don't know what rythem I should be hearing as a NEW ANDAIR pump during activation of on/off switch. The Dynon display with the red cube showed a fuel burn of 1.7 gal per hour on idle, forgot number on fuel pressure but it was in the green.

I noticed Aircraft Spruce is out of stock at both locations in US. Whether it's a popular item or Andair isn't supplying them anymore. With UK opting out, maybe a financial period looms. Don't know. My inspector says get it fixed by the tenth of July,after that he leaves for Oshkosh summer vacation. My option is drive 20 minutes up to Vans for their in stock fuel pump ( different brand).

Your thoughts, remedy , or go to Vans, or use a larger fuse?

Ron in Oregon.
My successful start up was due to all of you who over the past 6 years have offered your thoughts and pictures and most of all to Vansaiforce's founder and family and all the guardians of this website. I SAY THANKYOU,

[Ron B.]

I'm pretty sure I had to go to a 7.5 amp. fuse on mine. Haven't flown yet but have run the engine.

[ron sterba]

Thanks Ron, does your clicking from the pump seem to have same sequence in seconds?

[BillL]

Originally Posted by Ron B.

I'm pretty sure I had to go to a 7.5 amp. fuse on mine. Haven't flown yet but have run the engine.

Yep - 7.5A breaker for the vans pump.

I note the spec sheet for the Andair PX375 says 6 amps max, 4.5 nominal.

Hopefully, your wire size is adequate for a larger breaker/fuse.

[rv7charlie]

Hi Ron,

I have no direct experience with the Andair pump, but a couple of general thoughts.

Assuming it's the PX375, the spec sheet says '6 amps max' (note that it *doesn't* say '6 amp fuse'). That means that it can draw up to 6 amps (and likely will, in some situations). What the spec sheet doesn't say is that it's fairly likely it will have very short duration surge currents (typically during startup loading) higher than that.

The circuit drawing shows a 6 amp *circuit breaker*, not a fuse. Typical circuit breakers have a much longer time constant than typical automotive fuses. The automotive fuse is 'fast blow' and will blow, well, fast. It takes very little overload and a very short duration to blow it. A circuit breaker will have a much longer time constant (think 'slow blow') and will tolerate short term 'surge' currents significantly higher than its amp rating. So... if you replace your fuse with a 6A circuit breaker, you may find that everything works ok.

As a FWIW, the Andair document is inconsistent with good electrical practice. Good practice is to protect at around 20-25% above the maximum demand of the device, to avoid nuisance trips. So, if the pump really can draw '6 amps max' (and not just transient surges) in any normal mode of operation, then Andair has set up its users for nuisance trips.

Charlie

[Ron B.]

Originally Posted by ron sterba

Thanks Ron, does your clicking from the pump seem to have same sequence in seconds?

I cannot say I heard any clicking, but I do not have relays.

[bugsy63]

Hi Ron,
I had the same issue with my Andair pump when first activated in my 9A. If it's an early build, I believe mine is serial number 15, I read somewhere that the manufacturers didn't anticipate them sitting on a shelf for several years and didn't put a preservative lubricant in them. I solved my issue by capping off one end, filling it with av-gas, then capping the other, then leaving overnight. After draining the fuel and testing, the pump worked flawlessly. I can't recall the amperage on the VPX, but I think I've got a 10 amp breaker for the backup CB.

[ron sterba]

Charlie great food for thought, I'll try the 6 amp circuit breaker. I didn't know that about the fuses blowing quicker.

Ron in Oregon.

[Bevan]

Ron,

What size wire are you using to power the pump? Generally, we choose the wire size based on the requirements of the load (pump). Then we choose the value of the fuse/breaker to protect the wire.

Also, I believe fuses trip faster than breakers so there may be a consideration there too.

It would seem to me your fuse is significantly undervalued.

Bevan

[ron sterba]

Hi Michael, I like your thought for back up and a circuit breaker. Now Bill mentioned about the wire gauge, I'll have to check my list of AWG WIRES IN each CIRCUIT. IM GLAD I marked down all AWG wires for each circuit ( thanks to Joe Dubner EAA292). I tried to go heavy on gauges rather than adaquet for the unit usage. I'll check tomorrow my AWG list as tonight we are celebrating the 4 th of July.

Thanks

Ron in Oregon