Gland and groove dimensions

Cutting a new groove, or checking whether the one in front of you is the size it should be. All dimensions are inches. Groove width is called G, gland depth L, seal cross-section W and diametral clearance E.

Squeeze is the number that matters

A groove is right when it compresses the seal by the percentage in the table — too little and it weeps, too much and it takes a set and wears out early. Work from squeeze, not from the seal's free size.

O-ring glands, reciprocating

For rod and piston glands that move, to 1500 psi. Surface finish 32 microinch without a back-up ring, 63 with one. Break the corners to about a .005 radius.

Design table for industrial reciprocating O-ring packing glands
Size 2-	Section	Actual W	Gland depth L	Squeeze	%	Clearance E	G no back-up	G one	G two	Radius R	Ecc. max
006–012	1/16	.070 ±.003	.055–.057	.010–.018	15–25	.002–.005	.093–.098	.138–.143	.205–.210	.005–.015	.002
104–116	3/32	.103 ±.003	.088–.090	.010–.018	10–17	.002–.005	.140–.145	.171–.176	.238–.243	.005–.015	.002
201–222	1/8	.139 ±.004	.121–.123	.012–.022	9–16	.003–.006	.187–.192	.208–.213	.275–.280	.010–.025	.003
309–349	3/16	.210 ±.005	.185–.188	.017–.030	8–14	.003–.006	.281–.286	.311–.316	.410–.415	.020–.035	.004
425–460	1/4	.275 ±.006	.237–.240	.029–.044	11–16	.004–.007	.375–.380	.408–.413	.538–.543	.020–.035	.005

O-ring glands, static

For joints that do not move — gland-to-tube, port fittings, end caps. Squeeze runs higher than on a reciprocating gland because nothing has to slide. Halve the maximum clearance when the O-ring is silicone or fluorosilicone, and the gland depth may go up 5% to ease assembly when back-up rings are fitted.

Design table for industrial O-ring static seal glands
Size 2-	Section	Actual W	Gland depth L	Squeeze	%	Clearance E	G no back-up	G one	G two	Radius R	Ecc. max
004–050	1/16	.070 ±.003	.050–.052	.015–.023	22–32	.002–.005	.093–.098	.138–.143	.205–.210	.005–.015	.002
102–178	3/32	.103 ±.003	.081–.083	.017–.025	17–24	.002–.005	.140–.145	.171–.176	.238–.243	.005–.015	.002
201–284	1/8	.139 ±.004	.111–.113	.022–.032	16–23	.003–.006	.187–.192	.208–.213	.275–.280	.010–.025	.003
309–395	3/16	.210 ±.005	.170–.173	.032–.045	15–21	.003–.006	.281–.286	.311–.316	.410–.415	.020–.035	.004
425–475	1/4	.275 ±.006	.226–.229	.040–.055	15–20	.004–.007	.375–.380	.408–.413	.538–.543	.020–.035	.005

Urethane U-seal grooves

For loaded and unloaded U-cups. Groove width is the seal width plus 10%. Rod diameter equals the seal inside diameter; groove diameter equals the seal outside diameter. The clearance columns are the maximum diametral gap at that working pressure — go over it and the seal extrudes into the gap.

Rod and rod groove

Rod and rod groove diameters for urethane U-seals
Rod dia. range	Diameter tol.	Groove dia. tol.	1000 psi	3000 psi	5000 psi
.125–.687	+.0 / -.002	+.004 / -.0	.008	.006	.004
.750–2.875	+.0 / -.003	+.008 / -.0	.012	.008	.004
3.000–7.000	+.0 / -.004	+.010 / -.0	.014	.010	—
7.000–7.750	+.0 / -.005	+.011 / -.0	.016	.010	—
8.000–9.500	+.0 / -.005	+.012 / -.0	.016	—	—
10.000–15.000	+.0 / -.006	+.015 / -.0	.016	—	—

Bore and piston groove

Bore and piston groove diameters for urethane U-seals
Bore dia. range	Diameter tol.	Groove dia. tol.	1000 psi	3000 psi	5000 psi
.750–1.062	+.003 / -.0	+.0 / -.004	.010	.008	.004
1.125–1.625	+.003 / -.0	+.0 / -.005	.010	.008	.004
1.750–2.500	+.003 / -.0	+.0 / -.007	.012	.008	.004
2.625–2.875	+.003 / -.0	+.0 / -.008	.012	.008	.005
3.000–3.500	+.004 / -.0	+.0 / -.008	.014	.010	—
3.625–5.625	+.004 / -.0	+.0 / -.009	.014	.010	—
5.750–6.750	+.004 / -.0	+.0 / -.010	.014	.010	—
7.000–8.500	+.005 / -.0	+.0 / -.011	.016	.010	—
9.000–11.000	+.005 / -.0	+.0 / -.011	.016	—	—
12.000–16.000	+.006 / -.0	+.0 / -.012	.018	—	—

Extrusion gap

Pressure pushes seal material into whatever clearance is next to it. The maximum gap a urethane seal will bridge unaided is about .032" at 1000 psi, .012" at 3000 psi and .006" at 5000 psi. Past that it needs a back-up ring, or the bearings need replacing so the gap closes up.