Oil Pressure Sender Thread size

by Ian Rees in 912 / 914 Technical Questions 10 years ago

There have been a few different types of oil pressure sender units used on the 912. The thread sizes have also changed with the different senders.

What is the engine serial number for the 912UL design change from 1/8" NPT to metric M10 for the pressure sender on the oil pump housing? My engine S/N is 6770674, built 2012.

Is there a SB or other document which captures the change so owners can establish which thread is on which engine?

Re: Oil Pressure Sender Thread size

by Roger Lee » 10 years ago

Roger Lee

128 5.28k 4.98k

Hi Ian,

You have a fairly new engine and the new thread size. Yours is metric.
Older engines were US NPT threads.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Ian Rees

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Re: Oil Pressure Sender Thread size

by Rob Seaton » 10 years ago

Rob Seaton

3 1.32k 251

The information is in SI-912-020 Rev 8, Running mods.
see chapter 79-00-00

Thank you said by: Ian Rees

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Re: Oil Pressure Sender Thread size

by Ian Rees » 10 years ago

Ian Rees

6 42 0

Hello Roger and Rob,

Thank you both for your replies.

Could you please confirm the following data is correct for the 2 types of Pressure senders.

Honeywell,
4mA = 0 bar
20mA = 10 bar

Keller
4mA = 0.75 bar
20mA = 10.75 bar

Therefore, the senders are not directly interchangeable to instrumentation without some type of recalibration as the offset is different on the current output.

It seems that changing from a Honeywell type to the Keller type would cause a pressure reading error of 0.75 bar if applied to the same reading instrument. Is this correct?

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Re: Oil Pressure Sender Thread size

by Roger Lee » 10 years ago

Roger Lee

128 5.28k 4.98k

I thought the Honeywell and Keller were interchangeable?
I have not had to swap out one for the other yet.

Rob?

Keller is the currently used oil pressure sender. I'm sure there are a few Honeywell senders out there and a ton of VDO senders.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Oil Pressure Sender Thread size

by Ian Rees » 10 years ago

Ian Rees

6 42 0

Hi Roger,

There are 2 areas on compatibility, mechanical and electrical.

Mechanical is easy, both types are M10x1, so this is no issue.

Electrically, both are 4 to 20mA curent loop outputs.
However, the output transfer function is different.
My engine manual (912UL, 2012) shows the transfer function for the Honeywell type has a current of 4mA at 0 bar. 20mA at 10 bar.
The Keller unit transfer function is shown in the service instruction for the running change.
It has an offset of 0.75 bar at 4mA output. 20mA = 10.75 bar.

The full scale for both is 10 bar over 4mA to 20mA out. However the 4mA offset is different.
Hence, they are NOT interchanable. This means our instrumentation must be changed if the sender is changed.

I think this is potentially an issue for any aircraft with a sender unit which is changed.
The problem will cause a pressure reading error of 0.75 bar. This is very significant when compared to the minium pressure for normal operation of 1.8 bar.

Changing senders from one type to another could cause a engine running out of specification to be reading in or out of specification.

Could you please review my data analysis in this post and confirm the findings, thank you. If correct, it might be worth a Rotax video to explain the differences and affect on pressure gauges.

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