[KiloFoxtrot]

I have the Firewall Forward book by TONY BINGELIS and it shows a restrictor fitting (aka by Vans VA-128) in the line to the manifold pressure sensor.

Is this an old school thought?

Is it really needed and why?

Vans only shows the VA-128 being needed for fuel and oil pressure sensors.

Did you install the Manifold Pressure line with or without a restrictor fitting?

 

[BillL]

I got the restrictor fitting with my kit, and it is supposed to dampen the intake pulses and yield a more stable reading in the EFIS. It may just limit the extremes and allow the software to to the rest.

 

[wirejock]

Restrictor fitting

Tom ( TS Flightlines) sells a kit with all the plumbing lines and a nice restrictor fitting. I actually used more than one of his fittings.

 

[planenutz]

I've seen installations both with and without restrictors and while its not essential to have one, it's certainly what I consider to be "best practice" and highly recommended. The primary purpose of the restrictor is to reduce the effect of a broken MAP line on engine operation however the added benefit is the dampening of intake pulses through the line to the MAP gauge or sensor.

Ye Olde steam gauges are not usually so badly affected by pulses as they have a restrictor on the inlet line that is adjusted in the manufacturing/calibration process to ensure the MAP needle doesn't bounce around all over the place, whereas you might find some electronic MAP sensors are not so equipped and therefore might be more sensative to pulses if a restrictor isn't present.

 

[Richard Connell]

My RV7 IO360 no restrictor. No issues.
My RV10 MP borderline unusable without one.
Both G3X. Same sender.
Strange!

 

[TS Flightlines]

WE typically use -3 hose and hose ends for MAP hoses, especially with PMags/Sureflys/EIS. Yes---we have jump sized fittings to -4, so the hoses can connect to the plans build fittings. My reasoning was the normal restrictors are .040, and they are used now to dampen the cylinder pulses, especially with modern avionics sender units. Our -3 hose end stems have an ID of .079, after crimping. Thats a pretty good ID, and normally, a restrictor isnt needed. But, we've seen that not all sendors are created equal, and sometimes the restrictor helps that final little bit to satisfy the builder.

The old school theory of using the restrictors on oil and fuel pressure hoses to 'lessen' the amount of leakage should a hose fail, is somewhat obsolete IMHO. If you are using good quality teflon, normally rated at 3000 psi, then something very catastrophic would have to happen before the hose would fail. 303 and 306 rubber style hose are life limited, and the liners can deteriorate, creating leakage.

Oh---and normal restrictors are 45*. WE can make them in straight and 90* also to assist in custom creations.

Tom

 

[Freemasm]

My RV7 IO360 no restrictor. No issues.
My RV10 MP borderline unusable without one.
Both G3X. Same sender.
Strange!

Regardless of the readout, the sensor is experiencing these cycles; thus decreasing its life. With the relatively high cost of these, I'd still strongly consider protecting them from the high cycle pressure swings.