05 – Test Instruction 9.1.4 Pressure Drop¶

Source: OCP UQD Specification v2.0.0 §9.1.4, Table 5, Table 6, §15.3.3 · ISO 18869:2017 §13 Related: 02-Parameters.md · 03-Tests.md (test A6) · 04-Backlog.md

Reading guide: Text without marking is a requirement from the OCP specification or ISO 18869. Rows marked (internal proposal) are our own recommendations where the specification lacks data. They must be approved before the test is run.

1. Purpose¶

Determine the pressure drop across a mated UQD/UQDB pair as a function of flow, in both flow directions. From the measurements the following are calculated:

curve fit ΔP(Q) = A·Q² + B·Q (ΔP in psi, Q in L/min)
Cv at rated flow, which must lie within the Table 6 limits
ΔP at 100 % and 150 % of rated flow

2. Scope¶

Product	Configuration	Mated position
UQD02 / 04 / 06 / 08	UQD plug + UQD socket	Fully mated and latched
UQDB02 / 04 / 06 / 08	UQDB plug + UQDB socket	Fully mated, hard-stop
Hybrid 02–08 (if BS-002 = Yes)	UQD plug + UQDB socket	Fully mated, hard-stop

Samples: 5 pairs per product (n = 5 minimum). The pairs must be new or, if BS-003 allows, shared with other non-destructive 9.1 tests. Flow directions: S→P (socket to plug) and P→S (plug to socket), on the same pair.

3. Acceptance criteria¶

Size	Rated flow (L/min)	Rated flow (GPM)	Min Cv	Max Cv	Allowed ΔP at rated flow (psi)	(bar)
02	2.27	0.60	0.30	0.43	1.95 – 4.00	0.134 – 0.276
04	6.44	1.70	1.1	1.6	1.13 – 2.39	0.078 – 0.165
06	11.36	3.00	2.2	3.3	0.83 – 1.86	0.057 – 0.128
08	17.79	4.70	3.6	5.6	0.70 – 1.70	0.049 – 0.118

The ΔP interval is calculated from ΔP = SG·(Q/Cv)² with SG = 1.0. It is for orientation, not a separate requirement.

Pass if, for both flow directions: 1. The lowest Cv at rated flow of the 5 pairs is ≥ Min Cv (requirement of the specification). 2. The highest Cv at rated flow of the 5 pairs is ≤ Max Cv (Table 6; the test description does not mention this requirement, see MD-007).

A and B are reported without an acceptance limit (MD-002).

4. Test conditions¶

Parameter	Value	Source
Test medium	Water	§9.1.4
Fluid temperature	25 ± 5 °C	§9.1.4
SG (specific gravity)	0.997 at 25 °C, or measured temperature per table. Use the same value in all calculations and state it in the report.	MD-006 (internal proposal)
Flow points	At least 6 points between 25 % and 150 % of rated flow, including 100 %	§9.1.4
Directions	S→P and P→S	§9.1.4, §15.3.3
Mated position UQDB/Hybrid	Fully mated at hard-stop	§9.1.4
Alignment	Coaxial, no side load on the coupling (internal proposal)	–

4.1 Flow points¶

Use at least these six points: 25, 50, 75, 100, 125 and 150 %. More points, for example 37.5 and 62.5 %, improve the curve fit.

Point	%	UQD/UQDB02 L/min (GPM)	04 L/min (GPM)	06 L/min (GPM)	08 L/min (GPM)
Q1	25	0.57 (0.150)	1.61 (0.425)	2.84 (0.750)	4.45 (1.175)
Q2	50	1.14 (0.300)	3.22 (0.851)	5.68 (1.500)	8.90 (2.350)
Q3	75	1.70 (0.450)	4.83 (1.276)	8.52 (2.251)	13.34 (3.525)
Q4	100	2.27 (0.600)	6.44 (1.701)	11.36 (3.001)	17.79 (4.700)
Q5	125	2.84 (0.750)	8.05 (2.127)	14.20 (3.751)	22.24 (5.875)
Q6	150	3.41 (0.900)	9.66 (2.552)	17.04 (4.501)	26.69 (7.049)

Conversion: 1 GPM (US) = 3.78541 L/min. Allowed deviation from the set value (internal proposal): ± 2 % of the point's flow. The curve fit is made on the measured flow.

4.2 Expected ΔP measuring range (transducer sizing)¶

Size	Min ΔP @ 25 % (Max Cv)	Max ΔP @ 150 % (Min Cv)
02	0.12 psi (8 mbar)	9.0 psi (0.62 bar)
04	0.07 psi (5 mbar)	5.4 psi (0.37 bar)
06	0.05 psi (4 mbar)	4.2 psi (0.29 bar)
08	0.04 psi (3 mbar)	3.8 psi (0.26 bar)

The tare pressure drop is added to the gross measurement. At low flows the net signal is only a few mbar, so transducer resolution and zero stability are critical.

5. Equipment¶

5.1 Instruments¶

Instrument	Requirement	Proposal (internal)
Differential pressure transducer	Accuracy per ISO 18869:2017 §6.3	Range 0–1 bar diff (02) and 0–0.5 bar diff (04–08), or two transducers for low and high range. Accuracy ≤ ± 0.1 % FS.
Flow meter	Per ISO 18869 §6.3	Coriolis or magnetic inductive, 0.3–30 L/min, ≤ ± 0.5 % of reading
Temperature sensor	Per ISO 18869 §6.3	Pt100 in the flow upstream of the sample, ± 0.2 °C
Data logger	–	≥ 10 Hz, average over the stable period

Fill in the actual accuracy requirements from ISO 18869:2017 §6.3 here before the test is run. All instruments must have valid calibration, and the calibration date is noted in the protocol.

5.2 Test circuit¶

Per ISO 18869 Figure 13 (spec Figure 13):

 [4] Controlled   L1 ≥ 10·D     (2)  L2 ≥ 5·D    ┌────(1)────┐   L4 ≥ 10·D   (2)  L5 ≥ 5·D
 flow    ─────────────────────────●──────────────┤ QD (L3)   ├──────────────●───────────── → return
 (pump/                          │               └───────────┘               │
  control)                       └────────────[3] Differential pressure ─────┘
                                                      transducer + T sensor, flow meter

Pos	Description
1	Coupling under test (mated pair)
2	Pressure taps
3	Differential pressure transducer
4	Controlled fluid supply (pump + flow control, temperature control)
L1	≥ 10 × hose ID, straight, upstream of the first pressure tap
L2	≥ 5 × ID, from the upstream pressure tap to the coupling
L3	Length of the coupling including end fittings
L4	≥ 10 × ID, from the coupling to the downstream pressure tap
L5	≥ 5 × ID, after the downstream pressure tap

Figure 13 in the specification also shows a section labelled "L6", which is not in the key (ED-008). Follow the key above.

5.3 Hose/pipe and minimum straight lengths¶

Hose or pipe ID must correspond to the hosebarb size in Table 5, ± 10 %. The same ID is used for UQD and UQDB of the same size.

Size	Nominal ID	ID range (mm)	L1, L4 min (mm)	L2, L5 min (mm)	Velocity at 150 %
02	1/4" (6.35 mm)	5.72 – 6.99	64	32	≈ 1.8 m/s
04	3/8" (9.525 mm)	8.57 – 10.48	95	48	≈ 2.3 m/s
06	1/2" (12.70 mm)	11.43 – 13.97	127	64	≈ 2.2 m/s
08	5/8" (15.875 mm)	14.29 – 17.46	159	79	≈ 2.2 m/s

The lengths are calculated on nominal ID. With a different actual ID they are recalculated. Measure and document the real ID.

5.4 Connecting the sample¶

Connections must be made with the minimum number of adapter fittings.

Configuration	Plug side	Socket side
UQD	ORB stud (ISO 11926-3) → adapter with port per ISO 11926-1 → hosebarb with hose ID per 5.3	The socket's own hosebarb, directly in hose with ID per 5.3
UQDB	ORB stud → adapter port → hosebarb	ORB stud → adapter port → hosebarb
Hybrid	As UQD plug	As UQDB socket

Adapters ISO 11926-3 male stud → hosebarb (the specification's example):

End	ID (mm)	Tol.	Length (mm)	Tol.
11926 7/16	4.4	±0.08	9.1	±0.2
1/4 HB	4.4	±0.08	20.5	REF
11926 9/16	7.5	±0.1	10	±0.2
3/8 HB	7.5	±0.1	24.1	REF
11926 3/4	10	±0.1	11.1	±0.2
1/2 HB	10	±0.1	28	REF
11926 7/8	12.5	±0.1	12.7	±0.2
5/8 HB	12.5	±0.1	38	REF
11926 1-1/16	15.5	±0.12	15.1	±0.2
3/4 HB	15.5	±0.12	38	REF

Stud length 9.5 mm [0.38"]. Diameter per SAE J1926-3 / ISO 11926-3. Tighten to the torque in Table 5 (02-Parameters §6).

Combinations per size

Size	Plug stud (UQD/UQDB)	UQDB socket stud	Adapter plug side	Adapter UQDB socket side
02	7/16-20 (ORB-04)	9/16-18 (ORB-06)	11926 7/16 → 1/4 HB	11926 9/16 → 1/4 HB (*)
04	9/16-18 (ORB-06)	3/4-16 (ORB-08)	11926 9/16 → 3/8 HB	11926 3/4 → 3/8 HB (*)
06	3/4-16 (ORB-08)	7/8-14 (ORB-10)	11926 3/4 → 1/2 HB	11926 7/8 → 1/2 HB (*)
08	7/8-14 (ORB-10)	1-1/16-12 (ORB-12)	11926 7/8 → 5/8 HB	11926 1-1/16 → 5/8 HB (*)

(*) The specification's example table pairs each thread with a fixed HB size. The UQDB socket has a stud one size larger than the plug, but hose ID must be the same on both sides. That combination is not in the example. Produce the adapter internally with the ID per the table above.

5.5 Tare adapter (replaces the coupling during tare measurement)¶

Coupling	Thread 1	Diameter D (mm)	Length L (mm)	Thread 2	Length L2 (mm)
UQDB02 / UQDH02	7/16-20	9.88 ± 0.15	96 ± 5	9/16-18	14.5 ± 0.5
UQDB04 / UQDH04	9/16-18	12.92 ± 0.17	112 ± 5	3/4-16	16 ± 0.5
UQDB06 / UQDH06	3/4-16	17.5 ± 0.18	124 ± 5	7/8-14	18 ± 0.5
UQDB08 / UQDH08	7/8-14	20.48 ± 0.21	139 ± 5	1-1/16-12	20.5 ± 0.5

Threads per SAE J1926-1 / ISO 11926-1 (ports). The adapter replaces the coupling so that the same stud adapters remain on both sides.

UQDB: use the tare adapter per the table. Thread 1 receives the plug-side adapter and thread 2 the socket-side adapter.
UQD (hosebarb socket): the table does not cover this case (MD-015). (Internal proposal) Replace the coupling with a port per ISO 11926-1 (thread 1) on one side and a hosebarb of the same size as the socket's on the other, so that the plug adapter and the socket hose with clamp remain unchanged.
The column "Diameter D" is larger than the hose ID and probably refers to outside diameter (MD-021). It does not affect function.

Requirement: All hose, pipe and fittings between the pressure taps (2) and the coupling (1) must be identical in the test and tare set-ups.

6. Preparations¶

#	Step
F1	Check sample ID, marking and visual status per 03-Tests §3. Note the sample ID for each plug and socket.
F2	Measure and note the actual hose ID and the lengths L1–L5.
F3	Fit adapters to the sample terminations with torque per Table 5.
F4	Check the instruments' calibration dates and zero the differential pressure transducer at zero flow with a filled, bled circuit.
F5	Fill the circuit with water and bleed pressure taps and transducer lines. Air in the transducer lines gives large errors at small ΔP.
F6	Run water through the circuit until the temperature is stable within 25 ± 5 °C (internal proposal: ± 1 °C during a whole test series).
F7	Determine the stability criterion (internal proposal): flow ± 1 % and ΔP ± 1 % for 30 s, then average over 30 s.

7. Execution¶

7.1 Tare measurement (ISO 18869 §13.3)¶

Tare is measured once per size and configuration, and repeated if hose or adapters are changed.

#	Step
T1	Fit the tare adapter in place of the coupling, with the same hose and adapters as for the sample.
T2	Run flow points Q1–Q6 (same set values as for the sample).
T3	Record measured flow, temperature and ΔP_tare for each point.
T4	Measure in both directions if the set-up is not symmetric (internal proposal).
T5	Fit a second-degree polynomial ΔP_tare(Q) = a·Q² + b·Q, so that tare can be subtracted at the sample's actual flows.

7.2 Sample measurement (ISO 18869 §13.2)¶

Repeated for each pair 1–5 and both directions.

#	Step
P1	Mate the pair. UQD: check that the latch is engaged. UQDB/Hybrid: drive to hard-stop.
P2	Mount the pair in the circuit in direction S→P (fluid enters the socket and leaves through the plug).
P3	Bleed again and check the temperature.
P4	Set Q1, wait for stability and record Q, T and ΔP_gross.
P5	Repeat for Q2–Q6, in ascending order.
P6	(Internal proposal) Re-measure Q4 at decreasing flow as a check. The deviation must be ≤ 2 %.
P7	Turn the pair, or the circuit, to direction P→S and repeat P3–P6.
P8	Change to the next pair and repeat P1–P7.

8. Calculations¶

8.1 Net pressure drop (ISO 18869 §13.5)¶

For each measuring point i:

ΔP_net,i = ΔP_gross,i − ΔP_tare(Q_i)

ΔP_tare(Q_i) is taken from the tare curve at the actual flow Q_i.

8.2 Mean over samples¶

For each direction and flow point the mean of ΔP_net over the 5 pairs (n ≥ 5) is calculated. Plot net pressure drop against flow, one graph per direction, with both individual pairs and the mean.

8.3 Curve fit ΔP(Q) = A·Q² + B·Q¶

Least-squares fit without a constant term (the curve passes through the origin). Use Q in L/min and ΔP in psi.

| ΣQ⁴  ΣQ³ | |A|   | ΣQ²·ΔP |
| ΣQ³  ΣQ² | |B| = | ΣQ·ΔP  |

Do the fit for: - the mean curve per direction (reported in Table 15.3.3), and - each individual pair and direction (for Cv per pair, see 8.4).

Report A, B and R². Coefficients in other units, e.g. bar and L/min, may be given as a supplement.

8.4 Cv at rated flow¶

Cv = Q · √(SG / ΔP)      Q in GPM, ΔP in psi

Size	Q (GPM) in the formula
02	0.60
04	1.70
06	3.00
08	4.70

ΔP at rated flow is taken from the curve fit for the respective pair and direction (Q_rated in L/min inserted into A·Q² + B·Q). A small deviation from the set value then does not affect the result.
Calculate Cv for each of the 5 pairs and both directions.
Report the lowest Cv per direction and compare with Min Cv. Compare the highest Cv with Max Cv.

8.5 ΔP at 100 % and 150 %¶

From the mean curve per direction:

ΔP_100 = A·Q_rated² + B·Q_rated
ΔP_150 = A·(1.5·Q_rated)² + B·(1.5·Q_rated)

8.6 Worked example (UQD04, fictitious values)¶

Mean curve S→P: A = 0.040 psi/(L/min)², B = 0.050 psi/(L/min)

ΔP_100 = 0.040·6.44² + 0.050·6.44 = 1.659 + 0.322 = 1.981 psi
ΔP_150 = 0.040·9.66² + 0.050·9.66 = 3.733 + 0.483 = 4.216 psi
Cv     = 1.70 · √(0.997 / 1.981) = 1.70 · 0.7094 = 1.206

1.1 ≤ 1.206 ≤ 1.6 → Pass.

9. Protocol¶

9.1 Header data (per test series)¶

Field	Value
Product / size
Configuration (UQD / UQDB / Hybrid)
Sample ID pairs 1–5 (plug / socket)
Date, operator
Test medium, SG used	Water,
Hose: type, actual ID (mm)
L1 / L2 / L4 / L5 (mm)
Adapters (part no.)
Tare adapter (part no.)
Instruments (ID, calibration date)	ΔP: · Q: · T:
Deviations from the instruction

9.2 Raw data (one table per pair and direction)¶

Point	Set value (L/min)	Q measured (L/min)	T (°C)	ΔP gross (psi)	ΔP tare (psi)	ΔP net (psi)
Q1
Q2
Q3
Q4
Q5
Q6

9.3 Summary per §15.3.3¶

Flow (L/min / GPM)	Direction	Pair 1	Pair 2	Pair 3	Pair 4	Pair 5	Mean
Q1	S-P
Q2	S-P
Q3	S-P
Q4	S-P
Q5	S-P
Q6	S-P
Q1	P-S
Q2	P-S
Q3	P-S
Q4	P-S
Q5	P-S
Q6	P-S

The values are net pressure drop in psid (the template says "psi(g)", see ER-004). Flow is stated in both L/min and GPM (ER-005).

Direction	ΔP @ 100 % (psid)	ΔP @ 150 % (psid)	A	B	Min Cv (5 pairs)	Max Cv (5 pairs)	Meets Cv requirement? (Y/N)
S-P
P-S

10. Sources of error and tips¶

Air in transducer lines: the most common cause of unstable or too high ΔP at low flows. Bleed between each pair.
Temperature drift: viscosity changes about 2 %/°C and mainly affects the linear term B. Keep the temperature stable within the series.
Hose clamps and hosebarb (UQD socket): penetration or pinching changes the local pressure drop. Use the same clamp type and fitting in test and tare (MD-017).
Tare share: at low flows the tare can be large compared with the sample's ΔP. Check that the net value is larger than the transducer's uncertainty.
UQDB hard-stop: the pair must rest at hard-stop without preload that deforms it. Use a fixture that holds the mated length per 02-Parameters §4.
Direction change: preferably turn the sample and not the circuit, so that the same pressure taps and hose lengths are used.

11. Open points affecting the test¶

ID	Short description	Impact here
MD-002	A, B lack limits	Reporting only
MD-006	SG not stated	Used per section 4 above
MD-007	Verification of Max Cv unclear	Checked per section 3 above
MD-015	Tare for UQD hosebarb missing	Internal proposal in 5.5
MD-017	Hose type and clamping not stated	Determine before test
MD-021	Tare table "Diameter D" unclear	No functional impact
ER-004	ΔP stated in psi(g) in the template	Report psid
ER-005	Mixed units L/min and GPM	Report both
ED-008	"L6" in Figure 13 missing from the key	Follow the key
BS-002	Hybrid or not	Controls the scope
BS-003	Share samples with other tests	Controls sample consumption

Flow (L/min / GPM)	Direction	Pair 1	Pair 2	Pair 3	Pair 4	Pair 5	Mean
Q1	S-P
Q2	S-P
Q3	S-P
Q4	S-P
Q5	S-P
Q6	S-P
Q1	P-S
Q2	P-S
Q3	P-S
Q4	P-S
Q5	P-S
Q6	P-S

Flow (L/min / GPM)	Direction	Pair 1	Pair 2	Pair 3	Pair 4	Pair 5	Mean
Q1	S-P
Q2	S-P
Q3	S-P
Q4	S-P
Q5	S-P
Q6	S-P
Q1	P-S
Q2	P-S
Q3	P-S
Q4	P-S
Q5	P-S
Q6	P-S

Flow (L/min / GPM)	Direction	Pair 1	Pair 2	Pair 3	Pair 4	Pair 5	Mean
Q1	S-P
Q2	S-P
Q3	S-P
Q4	S-P
Q5	S-P
Q6	S-P
Q1	P-S
Q2	P-S
Q3	P-S
Q4	P-S
Q5	P-S
Q6	P-S